Utrasound probe and ultrasound elasticity imaging apparatus

ABSTRACT

An ultrasound diagnostic apparatus includes an ultrasound probe which transmits/receives an ultrasound wave with respect to a subject to be diagnosed, an ultrasound wave transmit section which transmits an ultrasound wave for driving the ultrasound probe, a pressing section which applies an external pressure to the subject, a displacement measuring section which obtains two tomographic image data different in time series from a reflected echo signal received from the ultrasound probe and measures a displacement of each part in the subject based on the two tomographic image data, an image generating section which generates an elastic image from elasticity information based on the displacement of each part measured by the displacement measuring section, and a display section which displays the generated elastic image. Further, a pressing decision section decides whether or not the pressing operation by the pressing section is proper.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 11/558,642, filed Nov. 30, 2005, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an ultrasound imaging apparatus and anultrasound probe of the apparatus, by which a tomographic image of atarget part in a subject is obtained by using ultrasound waves, andparticularly relates to an ultrasound elasticity imaging apparatus andan ultrasound probe of the apparatus, by which a distortion and amodulus of elasticity are calculated for each point in a subject basedon ultrasound received signal data of consecutive time-series frames todisplay an elastic image indicating the hardness of a tissue.

BACKGROUND ART

For ultrasound imaging apparatuses, the following methods are available:one method is to apply an external force to a subject via an ultrasoundwave transmit/receive surface of an ultrasound probe, determine adisplacement of each point in the subject by using a correlationoperation of ultrasound wave received signal data on a pair of adjacenttime-series frames, measure a distortion by performing spatialdifferentiation on the displacement, and form an image of distortiondata, and another method is to form an image of elastic modulus datasuch as a Young's modulus of a tissue from a stress distribution causedby an external force and distortion data (e.g., Japanese PatentApplication Laid-Open No. 5-317313 and Japanese Patent ApplicationLaid-Open No. 2000-60853). The external force applied to the subjectincludes pressing and depressing the subject. Hereinafter, the externalforce will be simply referred to as “pressing.” Ultrasound receivedsignal frame data at a given time reflects, as information, theconfiguration and arrangement of tissues in the subject at that time. Ina method for obtaining tissue elasticity information by using ultrasoundwaves, first by using ultrasound received signal data of a pair offrames obtained at regular time intervals, a displacement of each partof a tissue is calculated. The displacement is caused by a pressureapplied between the regular time intervals. Then, displacementinformation undergoes spatial differentiation, so that distortions arecalculated for all points in a region of interest (ROI) and an elasticimage is constructed and displayed. With an elastic image obtained basedon such distortion/elasticity modulus data (hereinafter, referred to aselastic frame data), the hardness of a tissue can be measured anddisplayed.

In order to obtain high-quality elastic image data, it is preferable toapply a pressure causing a tissue of interest to have a distortion ofabout 0.5% to 1%. In a time phase when a distortion within a properrange is not applied, extracted elastic image data is disturbed. Whenobtaining ultrasound received signal frame data of a pair of frames atregular time intervals, a high pressing speed at a certain time causeslarge distortion of a tissue at that time, and a low pressing speed at acertain time causes small distortion of a tissue at that time.Therefore, the quality of two or more elastic image data (particularlydistortion image data) obtained in a series of pressing processesdepends upon a pressing speed at a time when obtaining ultrasoundreceived signal frame data of a pair of frames for constituting theelastic image data.

In elasticity imaging using a conventional ultrasound imaging apparatus,a tissue of interest is manually pressed by an ultrasound probe. Thus,it is difficult to keep pressing within a pressing speed range suitablefor high image quality all the time in a series of pressing processes.Further, a pressing speed is not constant at respective times, so that aplurality of outputted elastic image data becomes temporallydiscontinuous and elastic images become discontinuous between frames.Further, it is not possible to avoid a movement of hands in the pressingprocess. A pressing direction varied between times also causesdiscontinuity of the elastic image data having been sequentiallyobtained. Therefore, the quality of an elastic image depends upon thetechnique of the operator.

At the time intervals for obtaining ultrasound received signal framedata, a tissue of interest is moved out of a measuring cross section bya pressure in the short axis direction of the probe, or displaced athigh speed in the long axis direction or pressing direction of theprobe, so that the tissue of interest may deviate from ROI set by theimaging apparatus. In this manner, due to an improper pressing directionor an excessive speed, ROI set by the imaging apparatus may have anerror (correlation operation error) region, in which a correctdisplacement cannot be calculated. In a deep region where transmittedultrasound waves can not reach due to attenuation and in a region withfew ultrasound reflectors (a cyst and a lesion having a liquid therein),ROI set by the imaging apparatus may have an error (correlationoperation error) region, in which a correct displacement cannot becalculated, because no received signal reflecting a property of thetissue of interest with sufficient intensity cannot be obtained.Moreover, ROI set by the imaging apparatus may include an error regionwhere the calculation of a displacement is insignificant, due to theshape of the ultrasound probe and the pattern of a tissue of interest,for example, in a region where the ultrasound probe is not in contactwith the subject. In these cases, a distortion image is not correctlydisplayed in the error region.

Furthermore, a region having a displacement close to 0 may be entirelydistributed in ROI set by the imaging apparatus due to a pressing speedof 0 or an insufficient pressing speed. Such pressing speeds occur whena pressure is not applied to a tissue of interest at time intervals forobtaining a pair of ultrasound received signal frame data and a pressingspeed on a tissue of interest is too low. In this case, a distortionimage indicating distortions calculated using the displacement has a lowcontrast over the ROI.

In elastic imaging using the conventional ultrasound imaging apparatus,an image is constructed and displayed for all the measuring points ofthe set ROI without evaluating whether data (distortion or modulus ofelasticity) outputted as an arithmetic result is worth displaying or not(reliability and quality of data). Therefore, even though imageinformation on a region calculated under improper conditions is notworth displaying, the image information cannot be discriminated frominformation worth displaying. As a result, an elastic image of one frameis constructed such that a region worth displaying and a region notworth displaying are mixed, reducing the reliability of an elasticimage.

In the conventional ultrasound imaging apparatus, whether a pressingoperation for applying an external force from a body surface to a livingtissue of the subject is proper or not is not considered. Hence, it isnot always possible to obtain a proper elastic image.

In other words, an elastic image is obtained by determining a modulus ofelasticity from a displacement (distortion) of each part of a livingtissue and a pressure or the like, and imaging a distortion patternqualitatively or a modulus of elasticity quantitatively based on framedata of two tomographic images different in time series. The tomographicimages have been obtained by applying an external force to a livingtissue. A distortion of each part of a living tissue varies according toa pressing operation including a pressure, a pressing speed, a pressingtime, a pressing direction and the like. Without a certain distortiondifference between adjacent two frames, a proper elastic image cannot begenerated.

Particularly, for simplicity, an external force is applied by pressingthe ultrasound probe to a body surface of the subject in many cases,though an external force may be applied by mechanical device. A pressingstate is considerably changed by the feeling of the operator, and thusit is not always possible to obtain a proper elastic image. Similarly,because of variations among subjects, even when an operation isperformed in a uniform pressing state, a proper elastic image cannot bealways obtained.

Further, a pressing direction and the way to press may cause lateraldisplacement on a living tissue. Also in this pressing operation, anelastic image may include disturbance (noise) caused by lateraldisplacement and a proper elastic image may not be obtained.

The present invention is devised in view of these circumstances. Anobject of the present invention is to provide an ultrasound imagingapparatus which can stably form a high-quality elastic image in a giventime phase during elastic imaging. An object of the present invention isalso to provide an ultrasound imaging apparatus, by which when typicaland ideal data is hard to obtain in elastic imaging, a region of imageinformation including an elastic value not worth displaying isrecognized as, e.g., noise, and an elastic image reflecting theinformation is constructed, high-quality elastic imaging is enabled.Moreover, an object of the present invention is to provide the operatorwith pressing operation information for obtaining a proper elasticimage.

DISCLOSURE OF THE INVENTION

In order to attain the object, the present invention relates to anultrasound probe comprising an ultrasound wave transmit/receive surfacecoming into contact with the contact surface of a subject, an ultrasoundwave transmit/receive section which transmits an ultrasound wave to thesubject via the ultrasound wave transmit/receive surface and the contactsurface and receives an ultrasound wave reflected in the subject, and apressing mechanism for performing a pressing operation for applying apressure to the contact surface perpendicularly to the ultrasound wavetransmit/receive surface via the ultrasound wave transmit/receivesurface.

The pressing mechanism preferably comprises a holding part held by anoperator, and an actuator for performing the pressing operation bychanging a distance between the ultrasound wave transmit/receive surfaceand the holding part.

The actuator preferably comprises a rack connected to one of theultrasound wave transmit/receive surface and the holding part, a pinionwhich is connected to the other of the ultrasound wave transmit/receivesurface and the holding part and engages with the rack, and a motor fordriving the pinion.

The actuator preferably comprises a cylinder connected to one of theultrasound wave transmit/receive surface and the holding part, a pistonwhich is connected to the other of the ultrasound wave transmit/receivesurface and the holding part and inserted into the cylinder, and a pumpfor feeding liquid to the cylinder.

It is preferable that the contact surface is disposed in the subject,the ultrasound wave transmit/receive surface is inserted into thesubject, and the pressing mechanism performs the pressing operation inthe subject.

The pressing mechanism preferably comprises a support surface cominginto contact with an opposed contact surface of the subject, the opposedcontact surface being opposed to the contract surface in the subject,and an actuator for performing the pressing operation by changing adistance between the ultrasound wave transmit/receive surface and thesupport surface.

The actuator preferably comprises a rack connected to one of theultrasound wave transmit/receive surface and the support surface, apinion which is connected to the other of the ultrasound wavetransmit/receive surface and the support surface and engages with therack, and a motor for driving the pinion.

The actuator preferably comprises a bag for supplying liquid between theultrasound wave transmit/receive surface and a surface of the ultrasoundwave transmit/receive section, and a pump for changing an amount of theliquid in the bag, and the ultrasound wave transmit/receive surfaceincludes a surface of the bag.

The bag preferably comprises a first part serving as the ultrasound wavetransmit/receive surface and a second part other than the first part.The second part comprises a shell which is lower in flexibility than thefirst part and regulates the moving direction of the first part.

The actuator preferably comprises a bag for supplying liquid between theultrasound wave transmit/receive surface and the support surface, and apump for changing an amount of the liquid in the bag.

The actuator preferably comprises a plurality of bags for supplyingliquid between the ultrasound wave transmit/receive surface and thesupport surface, and a pump for changing an amount of the liquid in eachof the plurality of bags. The direction of the pressing operation isselected from a plurality of directions by selectively using at leastone of the plurality of bags.

Preferably, the ultrasound probe further comprises a cylindrical casingfor storing the ultrasound wave transmit/receive section, and theactuator comprises a ring-like bag which supplies liquid between theultrasound wave transmit/receive surface and a surface of the ultrasoundwave transmit/receive section and is attached around the casing, and apump for changing an amount of the liquid in the bag. The ultrasoundwave transmit/receive surface includes a surface of the bag.

Preferably, the ultrasound probe further comprises a stopper which isattached around the bag and acts as the support surface.

Preferably, the ultrasound probe further comprises a pressure measuringsection for measuring a pressure applied to the contact surface, and apressure control section for controlling the pressing mechanismaccording to the pressure measured by the pressure measuring section.

Preferably, the pressing mechanism comprises a bag having liquid andperforms the pressing operation by changing an amount of the liquid inthe bag, and the pressure measuring section measures a pressure appliedto the contact surface by measuring a pressure of the liquid in the bag.

Preferably, the ultrasound probe further comprises a first casing forstoring the ultrasound wave transmit/receive section and a second casingfor storing the pressing mechanism. The first casing comprises a firstholding part held by the operator and the second casing comprises asecond holding part which is held by the operator and attached relativeto the first holding part. The pressing mechanism comprises an actuatorfor performing the pressing operation by changing a distance between theultrasound wave transmit/receive surface and the second holding part.

The pressing mechanism preferably comprises a holding part held by theoperator and a control switch which is disposed on a position enablingthe switch to be operable with a hand of the operator who holds theholding part and controls the pressing operation of the pressingmechanism.

Further, the present invention relates to an ultrasound elasticityimaging apparatus comprising the ultrasound probe, an ultrasound wavetransmitting section for outputting an ultrasound signal for driving theultrasound probe, a displacement measuring section which obtains twotomographic image data different in time series from a reflected echosignal received from the ultrasound probe and measures a displacement ofeach part in the subject based on the two tomographic image data, anelasticity modulus calculating section for calculating a modulus ofelasticity of a tissue of each part in the subject based on displacementdata of each part in the subject, the displacement data being measuredby the displacement measuring section, an image generating section forgenerating an elastic image based on a modulus of elasticity determinedby the elasticity modulus calculating section, and a display section fordisplaying the generated elastic image.

Preferably, the ultrasound elasticity imaging apparatus furthercomprises a pressing period control section for controlling a pressingperiod of the pressing mechanism according to a time interval of the twotomographic image data.

Moreover, the present invention relates to an ultrasound elasticityimaging apparatus comprising a signal processing section for processinga signal detected by an ultrasound probe coming into contact with asubject tissue to generate a tomographic image and a distortion elasticimage, a display value evaluating section for evaluating the displayvalue of the generated distortion elastic image based on various dataused in a process of generating the distortion elastic image, aninformation adding section for adding hue information or monochromeinformation to the distortion elastic image according to the evaluationresult of the display value evaluating section, and a display sectionfor displaying the tomographic image and the distortion elastic imageincluding information added by the information adding section.

Further, the present invention relates to an ultrasound elasticityimaging apparatus comprising an ultrasound wave transmit/receive sectionwhich transmits and receives an ultrasound wave to and from a subjectand outputs a reflected echo signal, a tomographic scanning section forrepeatedly obtaining ultrasound received signal frame data in thesubject including a kinetic tissue, with an ultrasound cycle by using areflected echo signal from the ultrasound wave transmit/receive section,a signal processing section for performing predetermined signalprocessing on the time-series ultrasound received signal frame dataobtained by the tomographic scanning section, a monochrome dataconverting section for converting time-series tomographic frame datafrom the signal processing section to monochrome tomographic image data,a displacement measuring section for generating, based on thetime-series ultrasound received signal frame data obtained by thetomographic scanning section, displacement frame data indicating amovement or displacement of each point on the tomographic image, apressure measuring section for measuring or estimating a pressure in abody cavity of a diagnosed part of the subject to generate pressuredata, a distortion/elasticity modulus calculating section for generatingelastic frame data indicating a distortion and a modulus of elasticityof each point on the tomographic image based on the displacement framedata and the pressure data, a display value evaluating section fordevaluating the display value of the elastic frame data based on variousdata used in a process of generating the elastic frame data, aninformation adding section for adding hue information or monochromebrightness information to the elastic frame data according to anevaluation result of the display value evaluating section, and a displaysection for displaying the monochrome elastic image data and the elasticframe data including information added by the information addingsection.

The information adding section preferably constructs elastic frame databy adding image information with a gradation to a region worthdisplaying and adding single image information to a region not worthdisplaying, the single information being different from the imageinformation added with the gradation to the region worth displaying, sothat both of the region are distinguishable on an image.

The information adding section preferably constructs elastic frame databy adding image information with a gradation to a frame worth displayingand adding single image information to a frame not worth displaying, thesingle information being different from the image information added withthe gradation to the region worth displaying, so that both of the regionare distinguishable on an image.

The display value evaluating section performs statistical processingusing, as a population, the element data of various data used for theprocess of generating the elastic frame data, and evaluates the displayvalue of the elastic frame data based on a statistical characteristic.

The display value evaluating section preferably evaluates the displayvalue of the elastic frame data based on the displacement frame dataoutputted from the displacement measuring section.

The display value evaluating section preferably evaluates the displayvalue of the elastic frame data based on the pressure data outputtedfrom the pressure measuring section.

The display value evaluating section preferably evaluates the displayvalue of the elastic frame data based on the elastic frame dataoutputted from the distortion/elasticity modulus calculating section.

Preferably, the display value evaluating section automatically sets atleast one of the position and range of a region of interest fordisplaying the elastic frame data, according to a display valueevaluation result of the elastic frame data.

The display section preferably displays only the monochrome tomographicimage data but does not display the elastic frame data according to anevaluation result of the display value evaluating section.

Moreover, the present invention relates to an ultrasound elastic imagingapparatus comprising a signal processing section for processing a signaldetected by an ultrasound probe coming into contact with a subjecttissue to generate a tomographic image and a distortion elastic image, adisplay value evaluating section for evaluating the display value of thegenerated distortion elastic image based on various data used in aprocess of generating the distortion elastic image, and a displaysection for displaying only the tomographic image but does not displaythe distortion elastic image according to an evaluation result of thedisplay value evaluating section.

Further, the present invention relates to an ultrasound elasticityimaging apparatus comprising an ultrasound probe for transmitting andreceiving an ultrasound wave to and from a subject, ultrasound wavetransmitting device for outputting an ultrasound signal for driving theultrasound probe, pressing device for applying an external force to thesubject, displacement measuring device which obtains two tomographicimage data different in time series from a reflected echo signalreceived from the ultrasound probe and measures a displacement of eachpart based on the two tomographic image data, an elasticity moduluscalculating section for calculating a modulus of elasticity of a tissueof each part based on displacement data of each part of the subject, thedisplacement data being measured by the displacement measuring device,image generating device for generating an elastic image based on amodulus of elasticity determined by the elasticity modulus calculatingdevice, and display device for displaying the generated elastic image,wherein the device further comprises pressing decision device foranalyzing the displacement data to decide whether a pressing operationof the pressing device is proper or not, and decision output device fordisplaying a decision result of the pressing decision device on thedisplay device.

As described above, whether a pressing operation is proper or not isimmediately displayed on the display device, and thus the operator canobtain a proper elastic image by adjusting a pressure operation withpressing device (e.g., probe) depending upon whether a displayedpressing state is proper or not. Further, whether a pressing operationis proper or not is decided by analyzing displacement data, and thus itis possible to decide the suitability of a pressing operation inconsideration of variations among subjects. Consequently, it is possibleto achieve elasticity imaging with excellent usability for the operator.

In this case, the pressing decision device determines a distortionfactor distribution in the tomographic image based on displacement data,and decides whether a pressing operation performed by the pressingdevice is proper or not depending upon whether the distortion factordistribution is within a proper range or not. Additionally or instead ofthis operation, the pressing decision device can determine a degree oflateral displacement in a tomographic image based on displacement data,and decide whether a pressing operation performed by the pressing deviceis proper or not depending upon whether the degree of lateraldisplacement is within a proper range or not. Moreover, the decisionoutput device outputs, through display or/and sound, a guidance forcorrecting a pressing operation based on a decision result.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an embodiment ofan ultrasound imaging apparatus according to the present invention;

FIG. 2 is an outside drawing showing a liner array ultrasound probe;

FIG. 3 is an outside drawing showing an ultrasound probe having apressing plate;

FIG. 4 is a diagram showing an ultrasound probe including an automaticpressing mechanism of a motor mechanism;

FIG. 5 is a diagram showing an ultrasound probe including an automaticpressing mechanism of a pump mechanism;

FIG. 6 is a diagram showing an ultrasound probe where an automaticpressing unit is attached;

FIG. 7 is a diagram showing an ultrasound probe comprising a pressuresensor;

FIG. 8 is a diagram for explaining the control of the automatic pressingmechanism according to pressure information obtained by a pressuremeasuring section;

FIG. 9 is an outside drawing of a transrectal ultrasound probe accordingto the embodiment of the present invention;

FIGS. 10 (a) and 10 (b) are diagrams showing an embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 11 (a) and 11 (b) are diagrams showing another embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 12 (a) and 12 (b) are diagrams showing another embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 13 (a) and 13 (b) are diagrams showing another embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 14 (a) and 14 (b) are diagrams showing another embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 15 (a) and 15 (b) are diagrams showing another embodiment of theautomatic pressing mechanism included in the transrectal ultrasoundprobe;

FIGS. 16 (a), 16 (b) and 16 (c) are diagrams showing another embodimentof the automatic pressing mechanism included in the transrectalultrasound probe;

FIG. 17 is a diagram showing an example of the operation of a bag shownin FIG. 15 (a);

FIG. 18 is a diagram showing another embodiment of the bag;

FIG. 19 is a block diagram showing an embodiment of a display valueevaluating section shown in FIG. 1;

FIG. 20 is a diagram showing an example of measurement result frame datastored in a frame memory circuit of FIG. 19;

FIG. 21 is a diagram showing an example of measurement quality framedata constructed by a measurement quality evaluating circuit of FIG. 19;

FIG. 22 is a block diagram showing another embodiment of the displayvalue evaluating section shown in FIG. 1;

FIG. 23 is a diagram showing an example of decision result frame dataconstructed by a display decision circuit of FIG. 22;

FIG. 24 is a diagram showing an example of specific numeric values ofthe decision result frame data shown in FIG. 23;

FIG. 25 is a block diagram showing an embodiment of a color scanconverter shown in FIG. 1;

FIG. 26 is a diagram showing an example of elastic hue frame dataconstructed by a hue information adding circuit of FIG. 25;

FIG. 27 is a diagram showing an example of the elastic hue frame databefore processing when the position and range of ROI is automaticallycontrolled;

FIG. 28 is a diagram showing an example of the elastic hue frame dataafter processing when the position and range of ROI is automaticallycontrolled;

FIG. 29 is a diagram showing an example of elastic hue frame data inwhich all element data is constructed with the same single color and theelastic image data of a frame is displayed without gradation processing;

FIG. 30 is a block diagram showing the configuration of anotherembodiment of an ultrasound imaging apparatus according to the presentinvention;

FIG. 31 is a flowchart showing the steps of obtaining an elastic imagein the ultrasound imaging apparatus of the embodiment shown in FIG. 30;

FIGS. 32 (a) to 32 (e) are diagrams showing an example of displayedimages according to the embodiment of FIG. 31;

FIG. 33 is a diagram showing an example of a distortion factordistribution used for deciding whether a pressing operation is proper ornot;

FIG. 34 is a flowchart for outputting as sound whether a pressingoperation is proper or not;

FIGS. 35 (a) to 35 (e) are diagrams showing an example of displayedimages according to the embodiment of FIG. 34;

FIG. 36 is a flowchart showing that an elastic image stored in cinememory is reproduced and displayed;

FIG. 37 is a block diagram showing a configuration around lateraldisplacement decision device according to the embodiment of the presentinvention;

FIG. 38 is a flowchart mainly showing the steps in the lateraldisplacement decision device;

FIG. 39 is a diagram showing a state of a displayed image according tothe embodiment of FIG. 37; and

FIG. 40 is a diagram for explaining a block matching method fordetecting lateral displacement.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will specifically describe examples of the presentinvention in accordance with the accompanying drawings. FIG. 1 is ablock diagram showing an embodiment of an ultrasound imaging apparatusaccording to the present invention. The ultrasound imaging apparatusobtains a tomographic image of a target part in a subject 1 by usingultrasound waves and displays an elastic image indicating the hardnessof a living tissue. As shown in FIG. 1, the ultrasound imaging apparatuscomprises an ultrasound probe 10 having an automatic pressing mechanism20, an ultrasound wave transmit/receive control circuit 201, atransmitter circuit 202, a receiver circuit 203, a phasing/addingcircuit 204, a signal processing section 205, a monochrome scanconverter 206, an image display 207, an ultrasound received signal framedata selecting section 208, a displacement measuring section 209, apressure measuring section 210, a distortion/elasticity moduluscalculating section 211, an elastic data processing section 212, a colorscan converter 213, a switching adder 214, a display value evaluatingsection 215, and a device control interface 216.

The ultrasound probe 10 is formed of a number of oscillators arrangedlike strips. The ultrasound probe 10 mechanically or electronicallyperforms beam scanning, transmits ultrasound waves to the subject 1, andreceives ultrasound waves reflected in the subject 1. The ultrasoundwave transmit/receive control circuit 201 controls time to transmit andreceive ultrasound waves. The transmitter circuit 202 drives theultrasound probe 10 to generate a transmission pulse for generatingultrasound waves, and sets, at a certain depth, a convergent point ofultrasound waves transmitted by a transmission phasing/adding circuitincluded in the transmitter circuit 202. The receiver circuit 203amplifies a reflected echo signal, which has been received by theultrasound probe 10, with a predetermined gain. The number of amplifiedreceived signals corresponding to the number of oscillators are inputtedas separate received signals to the phasing/adding circuit 204. Thephasing/adding circuit 204 is fed with the received signals having beenamplified by the receiver circuit 203, controls the phases of thesignals, and forms ultrasound beams for one or more convergent points.The signal processing section 205 is fed with the received signals fromthe phasing/adding circuit 204 and performs kinds of signal processingincluding gain correction, log compression, detection, edge enhancement,filter processing and the like.

The ultrasound probe 10, the ultrasound wave transmit/receive controlcircuit 201, the transmitter circuit 202, the receiver circuit 203, thephasing/adding circuit 204, and the signal processing section 205constitute ultrasound wave transmit/receive device. A tomographic imageis obtained by using the ultrasound probe 10 to scan the inside of thesubject 1 with an ultrasound beam in a fixed direction.

The monochrome scan converter 206 comprises tomographic scanning devicefor obtaining ultrasound received signal frame data of the subject 1,which includes a kinetic tissue, with an ultrasound cycle by using areflected echo signal outputted from the signal processing section 205of the ultrasound wave transmit/receive device and reading theultrasound received signal frame data with a cycle of a televisionsystem to display the data, and device for controlling the system, forexample, the monochrome scan converter 206 comprises an AD converter forconverting a reflected echo signal from the signal processing section205 to a digital signal, two or more pieces of frame memory for storingtomographic image data, which has been digitized by the AD converter, intime series, and a controller for controlling the operations thereof.

The image display 207 displays time-series tomographic image dataobtained by the monochrome scan converter 206, that is, a B-modetomographic image, and comprises a DA converter for converting, to ananalog signal, image data outputted from the monochrome scan converter206 through the switching adder 214, and a color monitor which is fedwith an analog video signal from the DA converter and displays thesignal as an image.

In the present embodiment, the ultrasound received signal frame dataselecting section 208 and the displacement measuring section 209 branchoff from the output of the phasing/adding circuit 204, the pressuremeasuring section 210 is provided in parallel with these sections, thedistortion/elasticity modulus calculating section 211 is provided in thesubsequent stage of the pressure measuring section 210 and thedisplacement measuring section 209, the display value evaluating section215 branches off from the output of the displacement measuring section209, the elastic data processing section 212 and the color scanconverter 213 are provided in the subsequent stage of thedistortion/elasticity modulus calculating section 211, and the switchingadder 214 is provided on the output of the monochrome scan converter 206and the color scan converter 213. The display value evaluating section215 and the color scan converter 213 can be freely controlled by anoperator or the like through the device control interface 216.

The ultrasound received signal frame data selecting section 208sequentially obtains, in frame memory included in the ultrasoundreceived signal frame data selecting section 208, ultrasound receivedsignal frame data sequentially outputted in time series from thephasing/adding circuit 204 with a frame rate of the ultrasound imagingapparatus (the obtained ultrasound received signal frame data will bereferred to as ultrasound received signal frame data N), selects one ofpast ultrasound received signal frame data N-1, N-2, N-3, . . . , N-Maccording to a control command of the ultrasound imaging apparatus (theselected frame data will be referred to as ultrasound received signalframe data X), and outputs a pair of ultrasound received signal framedata N and ultrasound received signal frame data X to the displacementmeasuring section 209. A signal outputted from the phasing/addingcircuit 204 is not limited to the ultrasound received signal frame data.For example, I and Q signals obtained by complex-demodulating anultrasound received signal may be used.

The ultrasound received signal frame data selecting section 208 obtainsperiod information between the selected pair of ultrasound receivedsignal frame data N and X, and the pressing operation of the automaticpressing mechanism 20 is controlled according to the period. Thefollowing will describe an example of the operations.

A period between the pair of ultrasound received signal frame data N andX selected by the ultrasound received signal frame data selectingsection 208 is determined according to the period of ultrasound receivedsignal frame data which is outputted from the phasing/adding circuit 204and inputted to the ultrasound received signal frame data selectingsection 208 and the number of ultrasound received signal frame datathinned out between the past ultrasound received signal frame data X andthe current ultrasound received signal frame data N, which constitutethe pair of ultrasound received signal frame data. For example, whenultrasound received signal frame data serving as the output of thephasing/adding circuit 204 has a period of 40 frames per second and aperiod between the pair of ultrasound received signal frame data becomes20 frames per second when the number of frames thinned out between thepair of ultrasound received signal frame data N and X is one. Theautomatic pressing mechanism 20 obtains period information between thepair of ultrasound received signal frame data N and X and controls thepressing speed of a pressing operation based on the obtained periodinformation.

For example, under the above conditions, when the period of ultrasoundreceived signal frame data serving as output from the phasing/addingcircuit 204 is 40 frames per second and a period between the pair ofultrasound received signal frame data N and X is 20 frames per second,it is assumed that a pressure is continuously applied at a pressingspeed V0 enabling a distortion of 0.7% which is suitable for high imagequality of a tissue of interest. Under these circumstances, when theperiod of ultrasound received signal frame data serving as output fromthe phasing/adding circuit 204 is changed to 20 frames per second by achange of the imaging conditions of the ultrasound imaging apparatus,the period between the pair of ultrasound received signal frame data Nand X is reduced by half to 10 frames per second. In this case, when apressure is still applied at the pressing speed V0, intermittence timebetween the ultrasound received signal frame data is doubled, and thus adistortion of the tissue of interest increases to 1.4%, which deviatesfrom a range of distortions suitable for high image quality. As aresult, continuously outputted elastic image data is disturbed. Hence,in the automatic pressing mechanism 20 of the present embodiment, periodinformation on ultrasound received signal frame data is obtained. Forexample, under the above circumstances, the pressing speed is reduced byhalf to V0/2. Hence, even when an ultrasound wave transmit/receiveperiod varies due to a change of the imaging conditions of theultrasound imaging apparatus, it is possible to automatically control apressing operation so as to have the optimum pressing speed forobtaining a high-quality elastic image.

The automatic pressing mechanism 20 can arbitrarily switch a pressingspeed, an amount of compression (amplitude) accumulated in continuouspressurization/decompression, and the setting of a pressing operation.The setting includes a pressure threshold value for stopping thepressing operation.

The displacement measuring section 209 performs one-dimensional ortwo-dimensional correlation processing based on the pair of ultrasoundreceived signal frame data selected by the ultrasound received signalframe data selecting section 208, measures a displacement or a movementvector (direction and size of a displacement) of each measuring point ona tomographic image, and generates displacement frame data. A method ofdetecting a movement vector includes a block matching method and agradient method which are disclosed in Japanese Patent ApplicationLaid-Open No. 5-317313. In the block matching method, an image isdivided into, e.g., blocks of N×N pixels, the previous frame is searchedfor a block most approximate to a block of interest in the currentframe, and predictive coding is performed with reference to the block.

The pressure measuring section 210 measures or estimates a pressureapplied to a target part of the subject 1. The pressure measuringsection 210 measures a pressure applied between the subject 1 and theprobe head of the ultrasound probe 10. For example, the pressuremeasuring section 210 can be configured as follows: a pressure sensorfor detecting a pressure applied to a rod-like member is attached to aside of the probe head, a pressure between the probe head and thesubject 1 is measured in a given time phase, and a measured pressure istransmitted to the distortion/elasticity modulus calculating section211. The kind of the pressure sensor is not particularly limited. Forexample, capacitance pressure sensors and wire resistance pressuresensors are available.

The distortion/elasticity modulus calculating section 211 calculates adistortion and a modulus of elasticity of each measuring point on atomographic image based on displacement frame data (movement amount) anda pressure which are outputted from the displacement measuring section209 and the pressure measuring section 210, generates numeric data(elastic frame data) of a distortion or a modulus of elasticity, andoutputs the data to the elastic data processing section 212. Forexample, in the arithmetic operation of a distortion in thedistortion/elasticity modulus calculating section 211, pressure data isnot necessary. A distortion is calculated by performing spatialdifferentiation on a displacement. For example, a Young's modulus Ym,one of moduli of elasticity, is determined by dividing a stress(pressure) on each arithmetic point by a distortion on each arithmeticpoint as expressed in the formula below:

Ym_(i,j)=pressure (stress)_(i,j)/(distortion_(i,j))

(i, j=1, 2, 3, . . . )

where indexes i and j represent the coordinates of frame data.

The elastic data processing section 212 performs various kinds of imageprocessing such as smoothing performed on elastic frame data from thedistortion/elasticity modulus calculating section 211 in a coordinateplane, contrast optimization, and smoothing in the time-axis directionbetween the frames, and outputs processed elastic frame data to thecolor scan converter 213.

The color scan converter 213 comprises hue information converting devicewhich is fed with elastic frame data outputted from the elastic dataprocessing section 212 and a command from the device control interface216 or an upper limit value and a lower limit value of a gradationselection range in elastic frame data outputted from the elastic dataprocessing section 212, and adds, as elastic image data, hue informationincluding red, green, and blue from the elastic frame data. For example,regarding a region measured with a large distortion in elastic framedata outputted from the elastic data processing section 212, the hueinformation converting device converts the corresponding region in theelastic image data to a red code. Regarding a region with a smalldistortion, the hue information converting device converts thecorresponding region in the elastic image data to a blue code. The colorscan converter 213 may be a monochrome scan converter. Regarding theregion measured with a large distortion, the corresponding region in theelastic image data may be increased in brightness. Regarding the regionmeasured with a small distortion, the corresponding region in theelastic image data may be reduced in brightness.

The switching adder 214 is fed with monochrome tomographic image datafrom the monochrome scan converter 206 and color elastic image data fromthe color scan converter 213, adds or switches images, and outputs onlyone of the monochrome tomographic image data and the color elastic imagedata or both of the image data after addition/combination. For example,as described in Japanese Patent Application Laid-Open No. 2000-60853, amonochrome tomographic image and a color or monochrome elastic imageobtained by the monochrome scan converter may be simultaneouslydisplayed on two screens. Further, for example, a color elastic imagemay be translucently superimposed and displayed on a monochrometomographic image. Image data outputted from the switching adder 214 isoutputted to the image display 207.

FIG. 2 is a diagram showing the appearance of an ordinaryone-dimensional linear array ultrasound probe. Elements of oscillatorswhich generate ultrasound waves and receive reflected echo are arrangedin alignment on an ultrasound wave transmit/receive surface 101 of theultrasound probe 10. The oscillators generally have the function oftransforming an inputted pulse wave or a transmitted signal of acontinuous wave into an ultrasound wave and transmitting the ultrasoundwave, and the function of receiving an ultrasound wave reflected fromthe inside of the subject 1, transforming the ultrasound wave into areceived signal, which is an electric signal, and outputting the signal.

FIG. 3 is an outside drawing of the ultrasound probe 10 for obtaining anelastic image with ultrasound waves. The ultrasound probe 10 comprises apressing plate 31 flush with the ultrasound wave transmit/receivesurface 101. When obtaining an elastic image, while transmitting andreceiving ultrasound waves through the ultrasound wave transmit/receivesurface 101, a pressing surface constituted of the ultrasound wavetransmit/receive surface 101 and the pressing plate 31 is brought intocontact with the subject 1 and the subject 1 is pressed by moving thepressing surface up and down to provide a target part of the subject 1with a stress distribution. The pressing surface may be manually movedup and down by the operator or the automatic pressing mechanism 20described below.

As an embodiment of the automatic pressing mechanism 20 for performingthe pressing operation of the ultrasound probe, FIG. 4 shows an exampleusing driving force of an actuator including a motor mechanism. In FIG.4, the automatic pressing mechanism 20 moves up and down a pressingstage 102, on which the pressing surface constituted of the ultrasoundwave transmit/receive surface 101 and the pressing plate 31 isseparated. The automatic pressing mechanism 20 is constituted of a rackand pinion. The rack and pinion have a pinion 42 on the rotating shaftof a motor mechanism 41 which is stored in a probe holding part 103 ofthe ultrasound probe 10 held by the operator, and a rack 43 on a supportmember 104 of the pressing stage 102. The motor mechanism 41 moves upand down the pressing stage 102 relative to the probe holding part 103through the rack and pinion in response to a control command from anexternal motor control section 44. In other words, when the operatorholds the probe holding part 103 to bring the pressing stage 102 intocontact with the subject 1, an actuator changes a distance between thepressing stage 102 and the probe holding part 103, so that a pressure isapplied to the subject 1 through the pressing stage 102. A switch 105 isan interface which allows the operator to operate the automatic pressingmechanism 20 (motor control section 44), and the switch 105 is disposedon a position where the switch 105 is operable with fingers of theoperator who holds the probe holding part 103. The operator can adjustthe turning on/off of the automatic pressing mechanism 20, a workingpressure, and a working period through the switch 105. The motormechanism 41 may be a mechanism using an electromagnetic motor, anultrasound motor, and so on. A mechanism for transmitting power from themotor mechanism 41 to the pressing stage 102 is not limited to the rackand pinion. For example, a cam may be provided in the motor mechanism 41to vertically drive the support member 104 according to the shape of thecam. Instead of a power transmission mechanism such as a rack andpinion, a direct-acting motor or the like may be directly connected tothe pressing stage 102 and driven.

As another embodiment of the automatic pressing mechanism 20, FIG. 5shows an example using driving force applied by a pump mechanism. InFIG. 5, the automatic pressing mechanism 20 is constituted of areciprocating cylinder 51 stored in the probe holding part 103 of theultrasound probe 10 held by the operator. The support member 104 of thepressing stage 102 is connected to a piston 511 of the cylinder 51. Thecylinder 51 is connected to a pump 53 via a tube 52, and the piston 511in the cylinder 51 is moved up and down by the pressure control of thepump 53. With this structure linked to the piston, the pressing stage102 is automatically moved up and down. The switch 105 is an interfacewhich allows the operator to operate the automatic pressing mechanism 20(pump 53). The switch 105 is disposed on a position where the switch 105is operable with fingers of the operator who holds the probe holdingpart 103. The working fluid of the pump mechanism is not particularlylimited. Water, oil, air or the like may be used.

In the foregoing embodiment, a motor mechanism for driving the pressingstage 102 and a driving mechanism such as a pump mechanism are providedon the side of the probe holding part 103. The driving mechanism may beprovided on the side of the pressing stage 102. The above explanationdescribed that the ultrasound probe 10 includes the automatic pressingmechanism 20. The automatic pressing mechanism 20 may be attached to theoutside of an existing ultrasound probe.

FIG. 6 is a diagram showing another embodiment of the automatic pressingmechanism 20 in which an operation similar to the driving of thepressing stage can be performed by attaching an automatic pressing unit60 to the outside of an existing ultrasound probe. The automaticpressing unit 60 comprises an ultrasound probe fixing mechanism 61 forholding the existing ultrasound probe 10 in a fixing manner and adriving mechanism 62 for linearly (vertically) driving the ultrasoundprobe fixing mechanism 61. The switch 105 is an interface which allowsthe operator to operate the automatic pressing mechanism 60. The switch105 is disposed on a position where the switch 105 is operable withfingers of the operator who holds the automatic pressing unit 60. Theultrasound probe fixing mechanism 61 comes into contact with the neck ofthe probe holding part 103 of the ultrasound probe 10 and holds theultrasound probe 10 in a fixing manner. The ultrasound probe 10 fixedthus by the ultrasound probe fixing mechanism 61 is similar to thepressing stage of FIG. 4. The probe holding part 103, that is, theultrasound probe 10 is moved up and down using a rack and pinionconstituted of a rack 63 on the support member 62 of the ultrasoundprobe fixing mechanism 61 and a pinion 65 on the rotating shaft of adriving mechanism (motor mechanism) 64. In FIG. 6, two gears 66 and 67for power transmission are provided between the rack 63 and the pinion65. A casing including the automatic pressing unit 60 is detachablyattached outside the casing of the existing ultrasound probe 10. Whenthe operator holds the automatic pressing unit 60, the ultrasound probe10 can be moved up and down as a pressing stage.

The following will describe an embodiment in which a pressure appliedfrom the pressing surface to the skin of the subject 1 is measured bythe pressure measuring section 210 and the operations of the automaticpressing mechanism 20 are controlled using pressure data. FIG. 7 is adiagram showing an embodiment of the ultrasound probe 10 comprising thepressure measuring section 210 for measuring a pressure applied betweenthe ultrasound wave transmit/receive surface 101 of the ultrasound probe10 and the skin of the subject 1. As shown in FIG. 7, the ultrasoundprobe 10 comprises the pressure measuring section 210 composed ofpressure sensors 71 to 76 disposed on the edge of the pressing plate 31.As shown in FIG. 1, a pressure between the pressing plate 31 and theskin of the subject 1 is measured in a given time phase by using theultrasound probe 10. Pressure data is outputted to the automaticpressing mechanism 20 and the distortion/elasticity modulus calculatingsection 211. In other words, the automatic pressing mechanism 20 of thepresent embodiment obtains pressure data measured by the pressuremeasuring section 210 and controls the pressing operation of theautomatic pressing mechanism 20 according to the pressure data. Thepressure measuring section 210 may obtain pressure data by measuring aload applied to the driving mechanism of the automatic pressingmechanism 20 and calculating, according to the load, a pressure appliedfrom the pressing surface to the skin of the subject 1.

The following will describe the case where the automatic pressingmechanism 20 and the pressure measuring section 210 are connected toeach other as shown in FIG. 1 and the operations thereof are controlled.FIG. 8 is a diagram showing an example of the automatic pressingmechanism 20 using driving force applied by the motor mechanism 41 ofFIG. 4. As shown in FIG. 8, the pressure data of the pressure sensors 71to 76 disposed on the edge of the pressing plate 31 is inputted to themotor control section 44 of the automatic pressing mechanism 20. Themotor control section 44 outputs a motor control signal corresponding tothe pressure data to the motor mechanism 41 and controls the motormechanism 41 to perform a desired pressing operation.

The automatic pressing mechanism 20 of the present embodiment makes itpossible to stop the operation of the automatic pressing mechanism 20when the pressure measuring section 210 receives a pressure equal to orlarger than a reference pressure, so that an excessive pressure is notapplied to the subject. In the case of an elastic image, it is knownthat a pressure range enabling a high-quality elastic image is presentand a pressure exceeding the upper limit value or a pressure lower thanthe lower limit value disturbs an elastic image. According to theautomatic pressing mechanism 20 of the present embodiment, when thepressure measuring section 210 measures a pressure equal to or largerthan a threshold value in a continuous pressing process, the operationsof the automatic pressing mechanism 20 can be controlled to switch thepressing process to a continuous decompressing process. Conversely, whenthe pressure measuring section 210 measures a pressure equal to orsmaller than a threshold value in a continuous decompressing process,the operations of the automatic pressing mechanism 20 can be controlledto switch the decompressing process to a continuous pressing process. Aproper pressing state can be kept all the time by repeating theseoperations. Hence, it is possible to efficiently obtain a high-qualityelastic image in a limited imaging time.

The following will describe an intra-corporeal ultrasound probe forobtaining an elastic image of the subject by using ultrasound wavesaccording to the embodiment of the present invention. Oral, transanal,transvaginal, and endovascular ultrasound probes are available for partsof the subject where the ultrasound probe is inserted. The presentinvention is applicable to any type of the ultrasound probes. Atransrectal probe inserted into a rectum through the anus of the subjectwill be discussed below as an example.

FIG. 9 is an outside drawing of a transrectal ultrasound probe 80according to the embodiment of the present invention. When the operatorholds a probe holding part 81 and inserts an insertion part 82 into therectum of the subject, the ultrasound wave transmit/receive surface 101comes into contact with the inner surface of the rectum of the subject.The pressing stage 102 comprising the pressing surface constituted ofthe ultrasound wave transmit/receive surface 101 and the pressing plate31 can move relative to the insertion part 82. The pressing stage 102 ispressed to the inner surface of the rectum of the subject by theautomatic pressing mechanism 20. The switch 105 is an interface whichallows the operator to operate the automatic pressing mechanism. Theswitch 105 is disposed on a position where the switch 105 is operablewith fingers of the operator who holds the probe holding part 81.

FIG. 10 (a) is a diagram showing an embodiment of the automatic pressingmechanism 20 included in the transrectal ultrasound probe 80. FIG. 10(b) is a diagram showing the transrectal ultrasound probe 80 of FIG. 10(a) in the direction of an arrow 10 (b). In this embodiment, as in theembodiment shown in FIG. 4, the action of the actuator including themotor mechanism 41, the pinion 42, and the rack 43 moves up and downmoves the pressing stage 102 relative to the insertion part 82 in FIG.10 (b). At this point, the insertion part 82 has a surface opposite fromthe pressing stage 102 and the surface is in contact with, as a supportsurface, an inner surface of the rectum of the subject. The innersurface is opposite from an inner surface facing an imaging target.Thus, when the actuator changes a distance between the pressing stage102 and the support surface, a pressure is applied to the inner surfacewhere the pressing stage 102 is in contact with the rectum of thesubject.

FIG. 11 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe 80.FIG. 11 (b) is a diagram showing the ultrasound probe 80 of FIG. 11 (a)in the direction of an arrow 11 (b). In this embodiment, a fluid issupplied or discharged to and from a bag 83 by a pump 53 and a tube 52,which are similar to those of the embodiment shown in FIG. 5, to expandor shrink the bag 83. Thus, the pressing stage 102 is vertically movedrelative to the insertion part 82 in FIG. 11 (a) and a pressure isapplied to an inner surface of the rectum of the subject. The pressingstage 102 is in contact with the inner surface.

FIG. 12 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe 80.FIG. 12 (b) is a diagram showing the ultrasound probe 80 of FIG. 12 (a)in the direction of an arrow 12 (b). In this embodiment, five systems ofpumps, tubes, and bags are provided as in the embodiment of FIGS. 11 (a)and 11 (b). Bags 83A, 83B, 83C, 83D, and 83E are expanded and shrunk bypumps 53A, 53B, 53C, 53D, and 53E and tubes 52A, 52B, 52C, 52D, and 52E.The bags 83A, 83B, 83C, 83D, and 83E are selectively expanded andshrunk, so that the pressing stage 102 can move relative to theinsertion part 82 in the directions of arrows A, B, C, D, and E of FIG.12 (b). Thus, it is possible to apply a pressure to the inner surface ofthe rectum of the subject in a direction desired by the operator.

FIG. 13 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe. FIG.13 (b) is a diagram showing the ultrasound probe of FIG. 13 (a) in thedirection of an arrow 13 (b). In this embodiment, bags 83A, 83B, 83C,83D, and 83E are attached outside an existing transrectal ultrasoundprobe as in the embodiment shown in FIGS. 12 (a) and 12 (b), and thebags are expanded and shrunk by five pumps (not shown) connected viatubes 52A, 52B, 52C, 52D, and 52E. The surfaces of the bags 83A, 83B,83C, 83D, and 83E act as support surfaces coming into contact with aninner surface of the rectum of the subject. The inner surface isopposite from an inner surface facing an imaging target. The bags 83A,83B, 83C, 83D, and 83E are selectively expanded and shrunk, so that theinserted part 82 can be entirely moved relative to the rectum of thesubject in the directions of arrows A, B, C, D, and E shown in FIG. 13(b). Thus, even when the transrectal ultrasound probe has no movablepressing stage, it is possible to apply a pressure to the inner surfaceof the rectum of the subject in a direction desired by the operator.

FIG. 14 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe. FIG.14 (b) is a diagram showing the ultrasound probe of FIG. 14 (a) in thedirection of an arrow 14 (b). In this embodiment, a ring-like bag 55 isattached outside an existing transrectal ultrasound probe, and a liquid(e.g., water, a physiological saline solution and so on) is supplied anddischarged to and from the bag 55 by a pump (not shown) connected via anopening 84 and a tube 52, so that the bag 55 is expanded and shrunk. Thebag 55 is in contact with the inner surface of the rectum of thesubject. Thus, by expanding and shrinking the bag 55, a pressure can beapplied to the inner surface of the rectum of the subject without movingthe ultrasound wave transmit/receive surface 101 relative to the innersurface of the rectum of the subject. The bag 55 is interposed betweenthe ultrasound wave transmit/receive surface 101 and the inner surfaceof the rectum of the subject. The bag 55 is filled with liquid and thusdoes not interfere with transmission/reception of ultrasound waves. Asurface of the bag 55 comes into contact with an inner surface of therectum in the direction of an imaging target of the subject and acts asan ultrasound wave transmit/receive surface. Another surface of the bag55 comes into contact with an inner surface of the rectum of thesubject, the inner surface being opposite from the inner surface facingthe imaging target. Another surface of the bag 55 acts as a supportsurface.

FIG. 15 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe. FIG.15 (b) is a diagram showing the ultrasound probe of FIG. 15 (a) in thedirection of an arrow 15 (b). In this embodiment, a stopper 85 isattached outside the ring-like bag 55 shown in FIGS. 14 (a) and 14 (b).With this configuration, it is possible to regulate the expandingdirection of the bag 55 and efficiently apply a pressure to the innersurface of the rectum of the subject. At this point, a surface of thestopper 85 comes into contact with an inner surface of the rectum of thesubject. The inner surface is opposite from an inner surface facing animaging target. The surface of the stopper 85 acts as a support surface.

FIG. 16 (a) is a diagram showing another embodiment of the automaticpressing mechanism 20 included in the transrectal ultrasound probe. FIG.16 (b) is a diagram showing the ultrasound probe of FIG. 16 (a) in thedirection of an arrow 16 (b). FIG. 16 (c) is a perspective view showinga bag 55 and a tube 52. In this embodiment, the bag 55 is attachedoutside an existing transrectal ultrasound probe with a fixing belt 86,and a liquid (water, a physiological saline solution, and so on) issupplied and discharged to and from the bag 55 by a pump (not shown)connected via the tube 52, so that the bag 55 is expanded and shrunk.The bag 55 is in contact with the inner surface of the rectum of thesubject. Thus, by expanding and shrinking the bag 55, a pressure can bedirectly applied to the inner surface of the rectum of the subject.Hence, the automatic pressing mechanism 20 can be attached to thetransrectal ultrasound probe which does not comprise the opening 84(FIG. 15 (a)) and the tube 52.

FIG. 17 is a diagram showing an example of the operations of the bag 55shown in FIG. 15 (a). FIG. 18 is a diagram showing another embodiment ofthe bag. According to the shape and elasticity of a tissue to be pressedby the bag 55, the bag 55 may be deformed in the lateral direction ofFIG. 17 in an expanding manner and a pressure may be applied to thetarget tissue with low efficiency. Thus, a bag 56 of FIG. 18 comprises ashell 57 for regulating the expanding direction of the bag 56. The shell57 requires lower elasticity than other parts of the bag 56. Forexample, the shell 57 is formed by the following methods: the shell 57is made thicker than the other parts of the bag 56, a net or the like isbonded to a part of the bag 56 so as to correspond to the shell 57, orthe shell 57 is formed of a different material having lower elasticitythan the other parts of the bag 56. Thus, it is possible to efficientlyapply a pressure to a target tissue.

In the above-described intra-corporeal ultrasound probe, the pressuremeasuring section 210 (FIG. 1) for measuring a pressure applied from thepressing surface to the subject and outputting pressure data may beconstituted of the pressure sensors provided on the edge of theultrasound wave transmit/receive surface 101 as shown in FIG. 7. Thepressure measuring section 210 may obtain pressure data by measuring aload applied to the driving mechanism of the automatic pressingmechanism 20 and calculating, according to the load, a pressure appliedfrom the pressing surface to the subject. When the automatic pressingmechanism 20 comprises a bag and a tube, the pressure measuring section210 may obtain pressure data by measuring the internal pressure of thebag or the tube.

In the intra-corporeal ultrasound probe, in the case where the actuatorchanges a distance between the probe holding part 81 and the ultrasoundwave transmit/receive surface 101, even when the support surface is notin contact with a surface opposite from a surface facing an imagingobject of the subject, a pressure can be applied to the subject.

With the automatic pressing mechanism 20 of the foregoing embodiment, itis possible to automatically apply a pressure to the subject at adesired constant speed in a fixed direction, thereby obtaining elasticimage data with high image quality at a given time. Further, it ispossible to keep reproducibility of a pressing operation.

The following will describe the display value evaluating section 215 ofthe present embodiment. The display value evaluating section 215 usesdisplacement frame data outputted from the displacement measuringsection 209, evaluates the value of image display for each measuringpoint in ROI, distinguishes between useless information and usefulinformation, and does not leave an image of the useless information(masks the useless information) in the end.

FIG. 19 is a diagram showing an example of the flow of data inputted andoutputted in the display value evaluating section 215 of the presentinvention. The display value evaluating section 215 comprises a framememory circuit 2151, a measurement quality evaluation circuit 2152, anda display decision circuit 2153.

The frame memory circuit 2151 obtains, as measurement result frame data,displacement frame data outputted from the displacement measuringsection 209, and outputs the data to the measurement quality evaluationcircuit 2152. The measurement quality evaluation circuit 2152 receivesthe measurement result frame data outputted from the frame memorycircuit 2151 and constructs measurement quality frame data whichreflects, as a numeric value, reliability of the measurement resultframe data, that is, whether a measurement result is normal or not oneach measuring point in ROI.

The following will discuss an example of the operations of themeasurement quality evaluation circuit 2152. The measurement qualityevaluation circuit 2152 performs statistical processing in which apopulation is the element data of measurement result frame data, andconstructs measurement quality frame data including a statisticalcharacteristic amount as element data. FIG. 20 is a diagram showing anexample in which measurement quality frame data is constructed based ona statistical characteristic amount.

First, as shown in FIG. 20, the element data of measurement result framedata is represented as X_(i,j) (i=1, 2, 3, . . . , N, j=1, 2, 3 . . . ,M). An index i corresponds to a coordinate in the horizontal axisdirection of an elastic image and an index j corresponds to a coordinatein the vertical axis direction. All element data included in ROI set bythe ultrasound apparatus are referred to with these indexes.

When element data, e.g., X_(4,4) is currently noticed and a kernel 2001of 3 (elements)×5 (elements) is set with coordinates X_(4,4) disposed atthe center. As a statistical characteristic amount with a population of15 element data in total distributed in the kernel 2001, for example, anaverage and a standard deviation are calculated as below:

(average)_(4,4)={Σ(measurement result frame data X_(i,j))}²/15{(standard deviation)_(4,4)}²=Σ{(average)_(4,4)−(measurementresult frame data X _(i,j))}²/15

(3≦i≦5, 2≦j≦6)

According to the above steps, (Standard deviation)_(i,j) is similarlycalculated for each element data X_(i,j), input is set as belowaccording to each element data Y_(i,j) of measurement quality framedata, and measurement quality frame data of FIG. 21 is generated.

(measurement quality frame data Y _(i,j))=(standard deviation)_(i,j)

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

Since displacement frame data is inputted as measurement result framedata, when an operation is performed and measurement quality frame datais constructed, element data Y_(i,j) constituting the measurementquality frame data has element data X_(i,j) of the same coordinates atthe center in displacement frame data and is fed with a value reflectingvariations in displacement (movement) with element data serving as apopulation. The element data is distributed in a region of a set kernelsize. The above measurement quality frame data is outputted to thedisplay decision circuit 2153.

In the foregoing embodiment, displacement frame data is inputted asmeasurement result frame data in the display value evaluating section215, and a region worth displaying and a region not worth displaying areevaluated. For example, as shown in FIG. 22, in thedistortion/elasticity modulus calculating section 211, elastic framedata generated by performing spatial differentiation on displacementframe data may be inputted as measurement result frame data in thedisplay value evaluating section 215. Since the elastic frame datareflects local discreteness of displacement frame data, it is possibleto achieve the same operation. The size of the kernel 2001 can be set atrandom. Further, the size of the kernel 2001 may be small around ROI.Processing such as spatial smoothing and smoothing between frames in thetime-axis direction may be performed on measurement quality frame data.

The display decision circuit 2153 is fed with measurement quality framedata outputted from the measurement quality evaluation circuit 2152, fedwith a threshold control signal 2161 outputted from the control sectionof the ultrasound apparatus via the device control interface 216, andperforms threshold processing in response to the threshold controlsignal 2161, so that decision result frame data indicating whether animage corresponding to a measuring point should be displayed or not isconstructed. The decision result frame data is outputted to the colorscan converter 213.

The following will describe an example of the operations of the displaydecision circuit 2153. The element data of measurement quality framedata reflects a standard deviation value of a displacement (movement)which is described in the explanation of the measurement qualityevaluation circuit 2152. Thus, decision result frame data can beconstructed by threshold decision on the element data of measurementquality frame data.

Regarding the element data of the measurement quality frame datagenerated by the measurement quality evaluation circuit 2152, as theelement data of the measurement quality frame data increases in value,variations in displacement distributed in a fixed region increase withthe coordinates of the element data at the center. Then, the displaydecision circuit 2153 sets, at a threshold value Th, the thresholdcontrol signal 2161 inputted from the ultrasound apparatus controlsection, and decides whether all element data constituting themeasurement quality frame data are larger than the threshold value Th ornot. For example, when element data Y_(i,j) of the measurement qualityframe data is larger than the threshold value Th, the display decisioncircuit 2153 sets “0” for element data Z_(i,j) of the same coordinatesof decision result frame data. When element data Y_(i,j) is smaller thanthe threshold value Th, the display decision circuit 2153 sets “1” forthe data Z_(i,j). Input is set as follows:

(measurement quality frame data Y _(i,j))>(threshold value Th)

(decision result frame data Z _(i,j))=0

(measurement quality frame data Y _(i,j))≦(threshold value Th)

(decision result frame data Z _(i,j))=1

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

Decision result frame data Z_(i,j) generated as a result is, forexample, configured as shown in FIG. 23.

With this threshold processing, decision result frame data isconstructed in which “0” or “1” is inputted to all element data Z_(i,j),and the decision result frame data is outputted to the color scanconverter 213. FIG. 24 is a diagram showing an example of decision framedata Z_(i,j) in which “0” or “1” is inputted to each element dataZ_(i,j).

In the foregoing embodiment, decision result frame data is generated inwhich a region worth displaying is set at “0” and a region not worthdisplaying is set at “1” in the display value evaluating section 215.The present invention is not limited to this example as long as thevalues are set so as to recognize whether a region is worth displayingor not.

The following will discuss an example of the operations of the colorscan converter 213 according to the present invention. FIG. 25 is adiagram showing an example of the flow of data inputted and outputted inthe color scan converter 213 of the present invention. The color scanconverter 213 comprises a frame memory circuit 2131, a gradationprocessing circuit 2132, a hue information adding circuit 2133, and animage constructing circuit 2134. The gradation processing circuit 2132comprises a rejection processing circuit.

The frame memory circuit 2131 obtains decision result frame dataoutputted from the display value evaluating section 215 as well aselastic frame data outputted from the elastic data processing section212, and outputs the data to the rejection processing circuit in thegradation processing circuit 2132.

The gradation processing circuit 2132 converts elastic frame data, whichis outputted from the frame memory circuit 2131 and has continuousvalues, into elastic gradation frame data having discrete values (e.g.,8 bits, 256 levels). This processing is performed by the rejectionprocessing circuit. The rejection processing circuit is fed with elasticframe data and decision result frame data from the frame memory circuit2131, and sets information on corresponding elements of elasticgradation frame data according to information on the elements ofdecision result frame data.

The following will discuss an example of the operations of the rejectionprocessing circuit in the gradation processing circuit 2132. In theelement data of decision result frame data, as values of decisionresults described in the operations of the display value evaluatingsection 215, “0” is set for a region less worth displaying and “1” isset for a region worth displaying as shown in FIG. 24. In this case, therejection processing circuit sets the element data of elastic gradationframe data of the corresponding coordinates at 8-bit values with 256levels according to the values of the element data of the decisionresult frame data.

In this setting, when the element data of elastic frame data correspondsto coordinates having a value of 0 as the element data of decisionresult frame data, the element data of the elastic frame data is uselessinformation. When the element data of elastic frame data corresponds tocoordinates of “1”, the element data is useful information. According tothe decision results, when the element data of elastic gradation framedata corresponds to coordinates having a value of “0” as the elementdata of decision result frame data, “0” is set for the element data ofthe elastic gradation frame data regardless of whether the values of theelement data of elastic frame data on the corresponding coordinates arelarge or not. When the element data of elastic gradation frame datacorresponds to coordinates having a value of “1,” as the element data ofdecision result frame data, values with 256 gray scales are setaccording to the values of the element data of the elastic frame data onthe corresponding coordinates. That is, an operation is performed asbelow:

(decision result frame data Z _(i,j))=0

(elastic gradation frame data T _(i,j))=0

(decision result frame data Z _(i,j))=1

(elastic gradation frame data T _(i,j))=(values “1” to “255”corresponding to S_(i,j))

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

where S_(i,j) represents the element data of elastic frame data inputtedfrom the frame memory circuit to the rejection processing circuit,Z_(i,j) represents decision result frame data, and T_(i,j) representsthe element data of elastic gradation frame data generated in therejection processing circuit.

This gradation processing constructs elastic gradation frame data where“0” to “255” of 256 levels are inputted to all element data T_(i,j).Elastic gradation frame data obtained by the gradation processingcircuit 2132 is inputted to the hue information adding circuit 2133.

The hue information adding circuit 2133 is fed with elastic gradationframe data outputted from the gradation processing circuit and generateselastic hue frame data according to information on each element of theelastic gradation frame data. The following will describe an example ofthe operations of the hue information adding circuit 2133. In theelement data of elastic gradation frame data, values are inputted asresults of the operations of the display value evaluating section 215and the gradation processing circuit 2132. For example, “0” is inputtedfor coordinates less worth displaying, and values from “1” to “255” of255 levels are inputted for coordinates worth displaying. In the hueinformation adding circuit 2133, for example, processing is performed toset hue information for the element data of elastic hue frame data onthe corresponding coordinates according to the values of the elementdata of elastic gradation frame data.

In this setting, when the element data of elastic frame data correspondsto coordinates having a value of 0 as the element data of elasticgradation frame data, the element data of the elastic frame data isuseless information. When the element data of elastic frame datacorresponds to coordinates of “1” to “255”, the element data is usefulinformation. According to the decision results, when the element data(R: red, G: green, B: blue) of elastic hue frame data corresponds tocoordinates having a value of “0” as the element data of elasticgradation frame data, for example, black (R=0, G=0, B=0) is set as hueinformation. When the element data of elastic hue frame data correspondsto coordinates having values of “1” to “255” as the element data ofelastic gradation frame data, for example, hue information of 255 levelsfrom blue to red is set according to the values of the element data ofthe elastic gradation frame data on the corresponding coordinates.

That is, operations are performed as below:

(elastic gradation frame data T _(i,j))=0

(elastic hue frame data U _(Ri,j))=0

(elastic hue frame data U _(Gi,j))=0

(elastic hue frame data U _(Bi,j))=0

(elastic gradation frame data T _(i,j))=1 to 255

(elastic hue frame data U _(Ri,j))=(T _(i,j)−1)

(elastic hue frame data U _(Gi,j))=0

(elastic hue frame data U _(Bi,j))=254−(T _(i,j)−1)

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

where T_(i,j) represents the element data of elastic gradation framedata inputted from the gradation processing circuit 2132 to the hueinformation adding circuit 2133, and U_(Ri,j), U_(Gi,j), and U_(Bi,j)represent the R (red) component, the G (green) component, and the B(blue) component of the element data of elastic hue frame data generatedin the hue information adding circuit 2133.

For example, FIG. 26 shows elastic hue frame data U_(ai,j) obtained byperforming the above processing according to decision result frame dataZ_(i,j) of FIG. 23. In FIG. 26, hue information cannot be illustrated.Thus, regions corresponding to elastic gradation frame data T_(i,j)=0are illustrated as white regions and regions corresponding to elasticgradation frame data T_(i,j)=1 to 255 are illustrated with gray scalesaccording to the values of the regions. With the addition of hueinformation, elastic hue frame data can be constructed in which thevalues of hue information of R, G, and B are inputted to all elementdata U_(ai,j). Elastic hue frame data to which hue information has beenadded by the hue information adding circuit 2133 is outputted to theimage constructing circuit 2134 of the subsequent stage.

In the present embodiment, regions worth displaying are displayed withgradation of blue to red and regions less worth displaying are displayedwith a single color of black. The present invention is not limited tothis example. A different method of allocating hues may be used as longas a region less worth displaying can be recognized as an image. Forexample, regions worth displaying may be displayed with gradation ofyellow to green and regions less worth displaying may be displayed witha single color of blue. In the present embodiment, the components ofelastic hue frame data were described using an RGB signal format. Thepresent invention is not limited to this example and may be achieved bya method of adding hue information in another signal format (e.g., YUV).Further, although the present embodiment describes an example in which aregion not worth displaying is identified with hue information differentfrom that of a region worth displaying in ROI, the present invention isnot limited to this example. For example, as shown in FIG. 27, whenregions not worth displaying are continuously present in two rows on theleft in the element data of elastic hue frame data U_(bi,j), the part ofthe regions is evaluated as a removal region. When a part is evaluatedas a removal region, the part is removed and ROI is reduced as shown inFIG. 28. ROI set and displayed by the ultrasound imaging apparatus isreduced, expanded, or moved, so that the removal region may beautomatically removed out of an ROI range set by the apparatus. FIG. 28shows an example in which two left rows corresponding to a region notworth displaying in FIG. 27 are removed and ROI is reduced.

The image constructing circuit 2134 is fed with elastic hue frame dataoutputted from the hue information adding circuit 2133 and fed with acontrol signal 2164 outputted from the control section of the ultrasoundapparatus through the device control interface 216. Accordingly, imageprocessing including interpolation such as polar coordinate conversion,scaling of an image, reversal and rotation of an image is performed onelastic hue frame data serving as original data, and elastic image dataconstituted of pixel data is generated. The image constructing circuit2134, the gradation processing circuit 2132, and the hue informationadding circuit 2133 are fed with the control signals 2162 to 2164through the device control interface 216. Whether functions should beaccepted or not is decided and the settings of operations are switchedand changed according to the control signals.

Incidentally, ultrasound received signal frame data at a given timereflects the structure and arrangement of living tissues at that time asinformation. In a method of obtaining tissue elastic information withultrasound waves, first, a pair of ultrasound received signal frame dataobtained at regular intervals is used to calculate a displacement ofeach living tissue. The displacement is caused by a pressure(pressurization, decompression) of a living tissue between fixed timeperiods. Then, spatial differentiation is performed on displacementinformation, so that a distortion is calculated on each point in ROI setby the ultrasound apparatus and an image is constructed and displayed.

However, at the site of actual imaging, ROI set by the imaging apparatusmay have an error (correlation operation error) region, in which acorrect displacement cannot be calculated, due to an improper pressingdirection or an excessive pressing speed, for example, in a first aspectwhere a tissue of interest is moved by a pressure in the short axisdirection of the probe and placed out of a measuring cross sectionduring a time interval when a pair of ultrasound received signal framedata is obtained, and in a second aspect where a tissue of interest isdisplaced by a pressure at high speed in the long axis direction or thepressing direction of the probe and placed out of a predetermineddisplacement operation range set by the imaging apparatus.

ROI set by the imaging apparatus may have an error (correlationoperation error) region, in which a correct displacement cannot becalculated, due to the absence of a received signal reflecting aproperty of a tissue of interest with sufficient intensity, for example,in a third aspect where a deep region not reached by any transmittedultrasound waves due to attenuation acts as a region of interest, and ina fourth aspect where a region with just a few ultrasound reflectors (acyst and a lesion having a liquid therein) acts as a region of interest.

In the first to fourth aspects, a region set as a region of interest(ROI) is likely to include a region having an incorrectly calculateddisplacement. When a distortion calculated using the displacement isdisplayed as an image, the region of interest of the distortion imageincludes incorrect information.

ROI set by the imaging apparatus may include a region where adisplacement is insignificantly calculated, due to the shape of theultrasound probe and the pattern of a tissue of interest, for example,in a fifth aspect where a region of interest is a region where theultrasound probe is not in contact with the subject. In the fifthaspect, a region set as a region of interest (ROI) includes a regionhaving an insignificant displacement. When a distortion calculated usingthe displacement is displayed as an image, a distortion image similarlyincludes incorrect and insignificant information.

In aspects represented by the first to fifth aspects, a first region anda second region discussed below are observed as a result of a tissuedisplacement made by a pressure. The first region is a region wheremeasuring points have equal displacements in the same direction (tissuesare locally combined with one another and collectively displaced in thesame direction), the second region is a region where a displacement anda direction vary between adjacent measuring points (tissues are notlocally combined with one another and adjacent tissues are discretelydisplaced in various directions). The two first and second regionsbroadly classified thus are observed in one displacement frame data.

In the first to fifth aspects, a region with an incorrectly calculateddisplacement and a region with an insignificantly calculateddisplacement are varied, like the second region, in displacement anddirection as displacement calculation results, and a region with aproper pressure becomes similar to the first region as a displacementcalculation result.

The foregoing embodiment described that displacement frame data is usedby the display value evaluating section 215 and the color scan converter213. In these operations, the following series of operations isperformed: displacement frame data is used to determine variations inlocal displacement, a measuring point with a large variation isevaluated as being less worth displaying, and a measuring point with asmall variation is evaluated as being worth displaying. Hue informationof black is added to a pixel of elastic image data corresponding to thecoordinates of the measuring point evaluated as being less worthdisplaying, and hue information consecutively changed from blue to redis added to a pixel of elastic image data corresponding to thecoordinates of the measuring point evaluated as being worth displaying,according to the value of an element of the corresponding coordinates ofmeasured elastic frame data. An elastic image is displayed on the screenof the ultrasound imaging apparatus. In the elastic image, elastic imageinformation on the measuring point less worth displaying is removed anda hue is added only to the measuring point worth displaying. Hence, onlya region where a proper pressure is applied is displayed with huegradation according to an elastic value. At the same time, a regionwhere no proper pressure is applied is displayed with no gradation suchthat an image can be identified by a single hue different from the huesof gradation.

With the display value evaluating section 215 and the color scanconverter 213 of the present embodiment, it is possible to stablyperform high-quality and reliable elastic imaging without being misleadby information on an insignificant elastic image region having not beenremoved, and simultaneously it is possible to feed back causes includingan improper operating method (pressing method, etc.) and device settingto the operator through an elastic image, thereby instantly providing anoperating method (pressing method, etc.) enabling a higher quality imageat the site of imaging.

According to the present embodiment, in the display value evaluatingsection 215, decision result frame data is generated in which ameasuring point worth displaying is set at “0” and a measuring point notworth displaying is set at “1”. Additionally, of all the elements (N×M)of decision result frame data, a ratio R of measuring points where theelements of decision result frame data are “1” may be determined by anoperation below:

(ratio R)=[Σ{(decision result frame data Z _(i,j))=1}](N×M)

When the determined ratio R is smaller than a reference ratio Rstd(e.g., 0.5), it is decided that just a few measuring points are worthdisplaying in a frame, and decision result frame data is generated againby resetting all the element data of the decision result frame data at“0” as follows:

(ratio R)<(reference ratio Rstd)

(decision result frame data Z _(i,j))=0

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

With this operation, in elastic gradation frame data T_(i,j) generatedby the color scan converter 213, all element data T_(i,j) are set at “0”according to the decision result frame data Z_(i,j). Thus, in elastichue frame data U_(ci,j), for example, all element data are constructedwith the same single color as shown in FIG. 29, and the elastic imagedata of a frame is displayed with no gradation. That is, elastic imagedata is not displayed. Hence, elastic image data is not displayed in thefifth aspect where a region of interest is a region in which theultrasound probe is not in contact with the subject, and additionally inan aspect where the operator searches for an affected part while movingan ultrasound probe head in contact with the subject along a body side.

In the foregoing embodiment, the display value evaluating section 215evaluates variations of elements within a local kernel size ofdisplacement frame data or elastic frame data serve as a population.Decision result frame data is generated in which a measuring point worthdisplaying is set at “0” and a measuring point not worth displaying isset at “1”. Different processing may be performed as follows:statistical processing is performed in which all the elements of theelement data X_(i,j) of measurement result frame data serve as apopulation, and an average M serving as a statistical characteristicamount is determined by an operation below:

(average value M)={Σ(measurement result frame data X _(i,j))}/(N×M)

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

When the average M is smaller than a reference average Mstd, it isdecided that just a few measuring points are worth displaying in aframe, and decision result frame data is generated again by resettingall the element data of the decision result frame data at “0” asfollows:

(average M)<(reference average Mstd)

(decision result frame data Z _(i,j))=0

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

With this operation, in elastic gradation frame data T_(i,j) generatedby the color scan converter 213, all element data T_(i,j) are set at “0”according to decision result frame data Z_(i,j). Thus, in elastic hueframe data U_(i,j), for example, all element data are constructed withthe same single color as shown in FIG. 29, and the elastic image data ofa frame is displayed with no gradation.

In the foregoing embodiment, the display value evaluating section 215makes evaluations in which the elements of displacement frame data, thatis, elastic frame data serve as a population. Decision result frame datais generated in which a measuring point worth displaying is set at “0”and a measuring point not worth displaying is set at “1”. Differentprocessing may be performed as follows:

Pressure data P outputted from the pressure measuring section 210 isinputted as measurement result frame data. When the pressure P issmaller than a reference ratio Pstd, it is decided that just a fewmeasuring points are worth displaying in a frame, and decision resultframe data is generated again by resetting all the element data of thedecision result frame data at “0” as follows:

(pressure P)<(reference pressure Pstd)

(decision result frame data Z _(i,j))=0

(i=1, 2, 3, . . . , N, j=1, 2, 3, . . . , M)

With this operation, in elastic gradation frame data T_(i,j) generatedby the color scan converter 213, all element data T_(i,j) are set at “0”according to decision result frame data Z_(i,j). Thus, in elastic hueframe data U_(i,j), for example, all element data are constructed withthe same single color as shown in FIG. 29, and the elastic image data ofa frame is displayed with no gradation.

When the pressure data P is obtained as Pi (i=1, 2, 3, . . . , N) in aone-dimensional distribution of the horizontal axis direction of animage, the pressure data P is compared with a reference pressure Pstdaccording to coordinates i. On coordinates not satisfying the referencepressure Pstd, decision result frame data Z_(i,j) of the correspondingcoordinates is set at “0”.

At the site of actual imaging, a region having a displacement close to 0is entirely distributed in ROI set by the imaging apparatus due to apressing speed of 0 or an insufficient pressing speed, for example, in asixth aspect where a pressure is not applied to a tissue of interestduring a time interval when a pair of ultrasound received signal framedata is obtained, and a seventh aspect where a pressing speed on atissue of interest is too low. To be specific, the operator searches foran affected part while moving the ultrasound probe head in contact withthe subject along a body side. Such a case corresponds to these aspects.In the sixth and seventh aspects, a region having a displacement closeto 0 is distributed over a region set as a region of interest (ROI).Thus, a distortion image displayed with a distortion calculated usingthe displacement is an image with no contrast or a low contrast over theset ROI. In aspects represented by the sixth and seventh aspects, firstand second frames discussed below are observed as a result of a tissuedisplacement made by a pressure.

A first frame is a frame where measuring points are not entirelydisplaced and no pressure is applied (an average of displacements orelastic values is 0) and a second frame is a frame where measuringpoints are entirely displaced just a little and only a low pressure isapplied (an average of displacements or elastic values is small). Thetwo first and second broadly divided frames may be observed in aplurality of elastic image frames in a series of pressing processes.

The foregoing embodiment described that displacement frame data orelastic frame data is used in the display value evaluating section 215and the color scan converter 213. In this operation, an average ofdisplacements or elastic values is determined. The overall elements ofdisplacement frame data or elastic frame data serve as a population. Aframe with an average determined to be lower than a predeterminedreference value is entirely evaluated as being less worth displaying.When an overall frame is decided to be less worth displaying, all theelastic image information of the frame is removed and elastic imageswhere a single hue is added with no gradation are collectively displayedon the screen of the ultrasound imaging apparatus. Only for a frame in atimes phase when a proper pressure is applied, an elastic image isdisplayed with levels of hues corresponding to the elastic values.Gradation is removed from a frame in a time phase when a proper pressureis not applied, and an image is displayed with a single hue differentfrom hues of gradation, so that it is possible to recognize a frame in atime phase when a proper pressure is not applied.

In the elasticity imaging method of the ultrasound imaging apparatus, animage is constructed and displayed for each frame in a given time phasewithout evaluating whether an elastic value (a distortion or modulus ofelasticity) outputted as an arithmetic result is worth displaying or not(evaluating image quality). Thus, at the site of actual imaging, eventhough image information calculated under improper conditions is a framenot worth displaying, the frame is not differentiated from a frame worthdisplaying, an elastic image of a series of consecutive frames isconstructed such that frames of both types are mixed. Consequently, thereliability of elasticity imaging decreases. In contrast, according tothe present invention, it is possible to stably perform high-quality andreliable elastic imaging without being mislead by information on aninsignificant elastic image frame having not been removed, andsimultaneously it is possible to feed back causes including an improperoperating method (pressing method, etc.) to the operator through anelastic image, thereby instantly searching for a pressing method or thelike enabling a higher quality image at the site of imaging.

Moreover, in a configuration where a color elastic image istranslucently superimposed and displayed on a monochrome tomographicimage, according to the present invention, an elastic image issuperimposed and displayed only during a pressing operation. In a timephase when a pressure is stopped, for example, the operator brings theultrasound probe head into contact with the subject and searches for anaffected part while moving the ultrasound probe head in contact with thesubject along a body side, elastic images are removed and thus onlymonochrome tomographic images are transmitted and displayed. Hence, itis possible to easily confirm a tomographic image on a measuring crosssection in a time phase other than elasticity imaging, therebyconsiderably improving efficiency of interpretation.

In the foregoing embodiment, region removal (region removing function)in one frame and removal over one frame (frame removing function) wereseparately described in detail. The present invention is not limited tothese operations. The two operations may be combined and performed atthe same time, and a configuration for the combined operations may beprovided.

The foregoing embodiment described that when the removal of a frame isdecided by the frame removal function according to an evaluation at thecurrent time, the image information on the frame at the current time isset at a single hue and displayed. The present invention is not limitedto this example. When the removal of a frame is decided at the currenttime, the closest past frame displayed without being removed may be keptand continuously displayed. This operation is not limited to the frameremoval function. The same function may be set for the operation of theregion removal function.

The foregoing embodiment described the display value evaluating section215 as an independent circuit. The present invention is not limited tothis configuration. The operation of the display value evaluatingsection 215 may be included in the color scan converter 213 or theelastic data processing section 212, or the order of processing circuitsmay be changed.

In the present embodiment, the operator can freely control, via thedevice control interface 216 included in the ultrasound apparatus, theselection of the region removal function and the frame removal function,the settings of a threshold value for threshold processing in theremoval function, a reference ratio, a reference average or the like,and the allocation and switching of hues added to a removed region and aremoved frame.

According to the present embodiment, even when ideal data is hard toobtain in elasticity imaging, a region of image information including anelastic value not worth displaying is recognized (as noise), an overallframe is recognized (as noise) when elastic values not worth displayingare calculated over the frame, and an elastic image reflecting theinformation is constructed, thereby providing an ultrasound imagingapparatus enabling high-quality elasticity imaging.

The following will describe the operations of the ultrasound imagingapparatus configured thus. First, according to ultrasound wavetransmission/reception control, a high-voltage electrical pulse isapplied from the transmitter circuit 202 to the ultrasound probe 10 incontact with the subject 1, an ultrasound wave is emitted, and areflected echo signal from an imaging target is received by theultrasound probe 10. The received signal is inputted to the receivercircuit 203 and preamplified therein. After that, the received signal isinputted to the phasing/adding circuit 204. To evaluate elasticity of apart of interest in a tissue of the subject by using the ultrasoundprobe 10 comprising the automatic pressing mechanism 20, the ultrasoundprobe 10 is brought into contact with the subject 1 while pressing thesubject 1 according to a proper pressing method automatically set by theautomatic pressing mechanism 20, so that consecutive ultrasound receivedsignal frame data are outputted from the phasing/adding circuit 204.

Received signals-aligned in phase in the phasing/adding circuit 204undergo signal processing such as compression and detection in thesubsequent signal processing section 205, and then the signals areinputted to the monochrome scan converter 206. The monochrome scanconverter 206 AD converts the received signals and stores the signals asa plurality of time-series consecutive tomographic image data in aplurality of frame memory in the monochrome scan converter 206.Ultrasound received signal frame data is successively outputted from thephasing/adding circuit 204 and inputted to the ultrasound receivedsignal frame data selecting section 208.

Of the ultrasound received signal frame data stored in the ultrasoundreceived signal frame data selecting section 208, a plurality oftime-series consecutive ultrasound received signal frame data areselected, inputted to the displacement measuring section 209, and aone-dimensional or two-dimensional displacement distribution (ΔL_(i,j))is determined. The displacement distribution is calculated by using, forexample, a block matching method as the method of detecting a movementvector. The method is not particularly limited. As in a generally usedmethod, a displacement may be calculated by calculating autocorrelationof two image data in the same region.

Period information between a pair of ultrasound received signal framedata selected by the ultrasound received signal frame data selectingsection 208 is outputted to the automatic pressing mechanism 20, and thepressing operation of the automatic pressing mechanism 20 is optimizedaccording to the period information. In the pressure measuring section210, a pressure applied to the subject 1 is measured, pressureinformation is transmitted from the pressure measuring section 210 tothe distortion/elasticity modulus calculating section 211 and theautomatic pressing mechanism 20, and the pressing operation of theautomatic pressing mechanism 20 is optically controlled according to thepressure information, so that elastic imaging can be efficientlyperformed on the subject.

The measurement signals of a displacement (ΔL_(i,j)) and a pressure(ΔP_(i,j)) outputted from the displacement measuring section 209 and thepressure measuring section 210 are inputted to the distortion/elasticitymodulus calculating section 211. A distortion distribution (ε_(i,j)) iscalculated by spatial differentiation (ΔL_(i,j)/ΔX) on a displacementdistribution (ΔL_(i,j)). Particularly, of modulus of elasticities, aYoung's modulus Ym_(i,j) is calculated by the formula below:

Ym_(i,j)=(ΔP _(i,j))/(ΔL _(i,j) /ΔX)

A modulus of elasticity on each measuring point is obtained by themodulus of elasticity Ym_(i,j) determined thus, and elastic frame datais generated.

The elastic frame data generated thus is inputted to the elastic dataprocessing section 212 and undergoes various kinds of image processingsuch as smoothing in a coordinate plane, contrast optimization, andsmoothing in the time-axis direction between frames.

The display value evaluating section 215 is fed with displacement framedata outputted from the displacement measuring section 209 or elasticframe data outputted from the distortion/elasticity modulus calculatingsection 211, evaluates whether an elastic image is worth displaying ornot on each measuring point or frame, generates evaluation result framedata according to the evaluation, and outputs the evaluation resultframe data to the color scan converter 213 or the monochrome scanconverter 206.

The elastic frame data outputted from the elastic data processingsection 212 and the evaluation result frame data outputted from thedisplay value evaluating section 215 are inputted to the color scanconverter 213 or the monochrome scan converter 206. According toinformation on the evaluation result frame data, removal is performed onuseless elastic information, and simultaneously useful information isconverted to hue information, which has undergone gradation processing,or monochrome brightness information.

Thereafter, a monochrome tomographic image and a color elastic image areadded and combined through the switching adder 214, or a monochrometomographic image and a color elastic image are sent to the imagedisplay 207 without additions. A monochrome tomographic image and acolor elastic image, which have undergone translucent processing, aresuperimposed and displayed on one screen, or a monochrome tomographicimage and a color elastic image are simultaneously displayed on the samescreen. The monochrome tomographic image is not particularly limited toan ordinary B-mode image. A tissue harmonic tomographic image formed byselecting harmonic components of a received signal may be used. A tissueDoppler image may be similarly displayed instead of a monochrometomographic image. Additionally, images displayed on two screens may beselected in various combinations.

The foregoing formation of an elastic image is an example where thedistortion or Young's modulus Ym of a living tissue is determined togenerate elastic image data. The present invention is not limited tothese parameters. For example, a modulus of elasticity may be calculatedusing other parameters including a stiffness parameter β, a pressureelastic modulus Ep, an incremental elastic modulus Einc (e.g., JapanesePatent Application Laid-Open No. 5-317313).

With this configuration, even when ideal data is hard to obtain inelasticity imaging performed by the ultrasound imaging apparatus of thepresent invention, a region of image information including a value ofelasticity not worth displaying is recognized as noise, an overall frameis recognized as noise when values of elasticity not worth displayingare calculated over the frame, and an elastic image reflecting theinformation is constructed, thereby providing an ultrasound imagingapparatus enabling high-quality elasticity imaging.

An elastic image may be kept without being rejected. The foregoingembodiment described that when the removal of a frame is decided by theframe removal function according to an evaluation of display value atthe current time, the image information of the frame at the current timeis set at a single hue and displayed. The present invention is notlimited to this example. When the removal of a frame is decided at thecurrent time, the closest past frame displayed without being removed maybe kept and continuously displayed. This operation is not limited to theframe removal function. The same function may be set for the operationof the region removal function.

Another embodiment of the present invention will be described below.FIG. 30 is a block structural diagram showing an ultrasound imagingapparatus of the present embodiment. FIG. 31 is a flowchart showing thesteps of obtaining an elastic image in the ultrasound imaging apparatusof the present embodiment. FIGS. 32 (a) to 32 (e) are diagrams showingan example of displayed images of the present embodiment.

As shown in FIG. 30, the ultrasound imaging apparatus of the presentembodiment comprises a probe 301 for transmitting and receivingultrasound waves to and from a subject, a tomographic image constructingsection 302 which captures a reflected echo signal outputted from theprobe 301 and reconstructs a tomographic image, and a display section303 for displaying the reconstructed tomographic image. Ultrasound wavetransmitting device for outputting an ultrasound signal for driving theprobe 301 is not illustrated. An elasticity calculating section 304includes displacement measuring device which sequentially captures theframe data of reflected echo signals inputted to the tomographic imageconstructing section 302 and measures a displacement of a tissue in eachpart of a tomographic image based on two tomographic image data adjacentto each other in time series, and elastic modulus calculating device forcalculating a modulus of elasticity of a tissue of each part based ondisplacement data of each part. The displacement data is measured by thedisplacement measuring device. The elasticity calculating section 304comprises pressing decision device for analyzing displacement data todecide whether a pressing operation is proper or not.

An elastic image constructing section 305 generates an elastic imagebased on the modulus of elasticity determined by the elasticitycalculating section 304, outputs the generated elastic image to thedisplay section 303, and stores the elastic image in cine memory 312.The decision results of a pressing operation decided by the elasticitycalculating section 304 are matched with respective elastic images,stored in pressing state memory 306, and outputted to an operationinformation output section 307. The operation information output section307 outputs the decision result of a pressing operation to the displaysection 303 and displays the results. The operation information outputsection 307 can output the decision result of a pressing operation assound through a sound output section 308.

Various operation commands and setting information inputted from anoperation input section 309 are inputted to a central processing section310, and the central processing section 310 controls a cine memory imagereproduction section 311 and so on in response to an inputted command orthe like.

Referring to the flowchart of FIG. 31 and examples of displayed imagesof FIGS. 32 (a) to 32 (e), the following will describe an operation ofobtaining an elastic image in the ultrasound imaging apparatusconfigured thus. First, as shown in FIG. 32 (a), at the start of ameasurement of an elastic image, a tomographic image 321 is outputtedfrom the tomographic image constructing section 302 to the displaysection 303 to display the tomographic image, and a dialog 322 forindicating a pressing state is displayed from the operation informationoutput section 307 to the display section 303 (S1). The dialog 322 has ahorizontally oriented display region like a bar chart. Two trianglemarks 323 a and 323 b are displayed along the display region. The mark323 a corresponds to the lower limit value of a proper range of apressing operation and the mark 323 b corresponds to the upper limitvalue of the range.

Then, the operator applies a pressure to the body surface of the subjectwith the probe 301 to apply a pressure to a living tissue (S2). In thispressing state, the tomographic image constructing section 302successively captures reflected echo signals and updates the tomographicimage of the display section 303 (S3). The elasticity calculatingsection 304 sequentially obtains frame data of a tomographic image fromthe tomographic image constructing section 302, measures a displacementof a tissue of each part based on two frame data adjacent to each otherin time series, calculates a modulus of elasticity of a tissue of eachpart based on measured displacement data of each part (S4), and outputsdata on the calculated modulus of elasticity to the elastic imageconstructing section 305 (S5). In step S4, the elasticity calculatingsection 304 analyzes displacement data to decide whether a pressingoperation is proper or not, and outputs the pressing state of a decisionresult to the pressing state memory 306 (S7). In this decision, forexample, as shown in FIG. 33, a distribution 331 of distortion factors Ein a tomographic image is determined based on displacement data, thatis, the distribution of the distortion factors ε is determined with ahorizontal axis representing a distortion factor of each pixel and avertical axis representing the number of pixels having a uniformdistortion factor. It is decided whether a pressing operation ofpressing device is proper or not depending on whether an average cm ofthe distortion factor distribution 331 is within the range of the upperand lower limit values (εH, εL) of the proper range. For example, inFIG. 33, distortion factor distributions 332 and 333 indicated by brokenlines are improper examples because averages are placed out of the upperand lower limit values (εH, εL). The distortion factor distribution 332is an example of a slow pressing speed. The distortion factordistribution 333 is an example of a fast pressing speed. For example, apressing state is judged according to eight evaluation levels, stored inthe pressing state memory 306, and outputted to the operationinformation output section 307.

The elastic image constructing section 305 constructs an elastic imageby color mapping based on elasticity modulus data outputted from theelasticity calculating section 304, and displays an elastic image 324superimposed on the tomographic image 321 of the display section 303 asshown FIG. 32 (b) (S7). The elastic image data is stored in the cinememory 312 (S8). Subsequently, the operation information output section307 obtains the evaluation level of a pressing state outputted from theelasticity calculating section 304 (S9), determines display of a stateof the dialog 322 according to the level, and outputs the indication ofa state to the display section 303 (S10). For example, as shown in FIG.32 (c), the display section 303 updates the indication of the dialog322. FIG. 32 (c) shows an example in which the evaluation level of apressing state exceeds the proper range. In response to the indicationof the dialog 322, the operator reduces the pressing speed, therebyobtaining a proper elastic image of FIG. 32 (d) according to theadjusted pressing speed during the subsequent elastic image formationperformed back in step S2 of FIG. 31. Therefore, as shown in FIG. 32(e), the indication of the state of the dialog 322 is within the properrange of the marks 323 a and 323 b, indicating that a proper elasticimage is obtained. In FIGS. 32 (a) to 32 (e), the marks 323 a and 323 bof the dialog 322 correspond to the upper and lower limit values (εH,εL) of the proper range.

In this way, according to the present embodiment, the dialog 322immediately indicates whether a pressing operation is proper or not. Theoperator adjusts the operation of the probe 301 depending upon whether apressing state indicated by the dialog 322 is proper or not, therebyreadily performing a pressing operation for obtaining a proper elasticimage. In addition, the present embodiment makes it possible to decidewhether a pressing operation is proper or not in consideration ofvariations among subjects, and thus the operator can perform a properpressing operation with great ease.

In the foregoing embodiment, the display section 303 displays whether apressing operation is proper or not through the dialog. The presentinvention is not limited to this example. Whether a pressing operationis proper or not may be outputted as sound. FIG. 34 is a flowchart foroutputting as sound whether a pressing operation is proper or not. FIGS.35 (a) to 35 (e) show an example of displayed images in this case. InFIG. 34, step S21 is similar to steps S2 to S8 of FIG. 31. The operationinformation output section 307 obtains the evaluation level of apressing state outputted from the elasticity calculating section 304(S22) and decides whether the evaluation level is appropriate (proper)or not (S23). When the evaluation level is proper, processing iscompleted. When the evaluation level is not proper, it is decidedwhether the evaluation level is “fast” or “slow” out of the properrange, and an evaluation result is set at sound of “fast” or “slow”(S25, S26). Thus, a sound output command of “fast” or “slow” isoutputted from the operation information output section 307 (S27), andan evaluation result, i.e., operation information is outputted as asound designated by the sound output section 308. FIGS. 35 (a) to 35 (e)show an example of displayed images.

In this way, according to the present embodiment, the operator canobtain operation information through sound without viewing displayedimages. Thus, it is possible to easily perform a pressing operation forobtaining a proper elastic image.

FIG. 36 is a flowchart showing the reproduction and display of anelastic image stored in the cine memory 312 of FIG. 30. When theoperation input section 309 instructs the CPU 310 to reproduce the cinememory (S31), the CPU 310 outputs a cine memory reproduction command tothe cine memory image reproduction section 311 (S32). Hence, the cinememory image reproduction section 311 obtains an elastic image from thecine memory 312 (S33) and obtains the evaluation result of a pressingstate in synchronization with an elastic image read from the pressingstate memory 306 (S34). Then, it is decided whether the read pressingstate is appropriate or not (S35). When the pressing state is notappropriate, the processing is completed. When the pressing state isappropriate, the CPU 310 outputs a command for instructing the displaysection 303 to display an elastic image reproduced by the cine memoryimage reproduction section 311 (S36). Thus, an elastic image stored inthe cine memory 312 is displayed on the display section 303 (S37). Thatis, only a proper elastic image stored in the cine memory 312 isreproduced and displayed.

The present embodiment provides operation information on whether apressing speed is proper or not. The present invention is not limited tothis example. Operation information can be provided in the event of apressing operation causing lateral displacement of a living tissue. Inother words, even when a pressing speed is constant over time periods ina process of a pressing operation, the subject is not always pressedevenly in the vertical direction over the time periods (hereinafter,referred to as time phases). For example, in a time phase when thesubject is pressed diagonally or unevenly, the stress distribution of aliving tissue becomes discontinuous in some time phases. In such timephases, coordinate regions appear which are discontinuous relative totime changes. Thus, an obtained elastic image includes a temporallydiscontinuous region as disturbance (noise), so that elasticity imagingcannot be properly performed. In other words, when lateral displacementoccurs, which is a lateral movement of a living tissue, due to an unevenpressure in the vertical direction, elasticity imaging cannot beproperly performed.

In the present embodiment, when a pressing operation causes lateraldisplacement of a living tissue, the lateral displacement is detectedand operation information is provided. The present embodiment can beachieved by replacing the pressing decision device constituting theelasticity calculating section 304 in the embodiment of FIG. 30 withlateral displacement decision device 338. In other words, as shown inFIG. 37, from displacement measuring device 339 for capturing frame dataof ultrasound received signal data from the tomographic imageconstructing section 302 and measuring a displacement, displacement datais captured to decide a degree of lateral displacement and a decisionresult is stored in the pressing state memory 306. In FIG. 37,elasticity modulus calculating device 340 calculates a modulus ofelasticity of each part of a tissue based on displacement data and is afunction included in the elasticity calculating section 304 of FIG. 30.

FIG. 38 is a flowchart mainly showing steps in the lateral displacementdecision device 338 of the present embodiment. When an elasticityimaging mode is turned on from the operation input section 309 to thecentral processing section 310, as shown in FIG. 39, the display section303 displays an ROI 336 for determining an elastic image for atomographic image 335, and a color map 337 indicating a modulus ofelasticity (S41). Then, the displacement measuring device 339 capturesfrom the tomographic image constructing section 302 a pair of frame dataadjacent to each other in time series (S42), measures a displacement ora movement vector (direction and size of a displacement) of each pixelon the tomographic image through correlation processing and so on, anddetects a lateral displacement (S43 to S45).

For example, a well-known block matching method is applicable tocorrelation processing in the displacement measuring device 339. In theblock matching method, an image is divided into blocks of N×N pixels (Nis a natural number), the previous frame is searched for a block mostapproximate to a block of interest in the current frame, and predictivecoding is performed with reference to the block. As shown in FIG. 40, ablock composed of N×N pixels is a correlation window 341 and a regionincluding a plurality of blocks of N×N pixels is a search range 342. Theblock having been referred in the previous frame is a point mostcorrelated to the block of the current frame. For simple explanation,the search range 342 has a size of nine correlation windows 341 as shownin FIG. 40. To be specific, blocks identical in size to the correlationwindow 341 are arranged around the correlation window 341 in thehorizontal and vertical directions and the diagonal directions. Thecorrelation window 341 and the search range 342 can be set at random.Assuming that a stress from the probe is evenly applied to the subjectin the vertical direction, the current frame and the previous frame aremost correlated on blocks 2 and 8 disposed on and under the correlationwindow 341 at the center of FIG. 40. When a stress from the probelaterally moves a tissue of the subject, blocks 4 and 6 disposed on bothsides of the correlation window 341 are most correlated (blocks 1, 3, 7,and 9 may be included). Then, a correlation operation is performed onnine blocks to determine the position of the most correlated block inone search range 342. In this correlation operation, for example, whenthe blocks 2 and 8 on both sides are most correlated, it is decided thatlateral displacement occurs and a lateral displacement counter countsthe displacement. In this way, correlation processing is performed ontarget data in ROI to calculate a displacement in ROI and a count C ofthe lateral displacement counter. Since data in ROI is divided by thesearch range 342, the number A of divided search ranges 342 is alsocalculated. The displacement in ROI is sent to the elasticity moduluscalculating device 340, and the count C of the lateral displacementcounter and the number A of divided search ranges 342 are sent to thelateral displacement decision device 338.

The lateral displacement decision device 338 decides the presence orabsence of lateral displacement based on the inputted A and C (S46). Thedecision is made depending upon whether A/X<C is established where Xrepresents an empirically fixed threshold value. When A/X<C isestablished, it is decided that a force is evenly applied to the subjectin the vertical direction. In this case, a lateral displacement flag isset at “0” and stored in the pressing state memory 306 (S47). When A/X<Cis not established, it is decided that a force is not evenly applied tothe subject in the vertical direction and a living tissue is laterallydisplaced. In this case, a lateral displacement flag is set at “1” andstored in the pressing state memory 306 (S52). For example, as shown inFIG. 39, the contents of the pressing state memory 306 is indicated as awarning “laterally displaced” on the lower side of the tomographic image335 (S56).

Meanwhile, the elasticity modulus calculating device 340 calculatesdistortion data S based on a displacement B measured by the displacementmeasuring device 339 (S48, S53), and the elastic image constructingsection 305 of FIG. 30 performs gradation processing on the distortiondata S to construct an elastic image, and displays the elastic image onthe display section 303.

Hence, according to the present embodiment, the operator can confirm howthe force of the probe is applied to the subject in real time. In theevent of lateral displacement, the operator can adjust the operation ofthe probe in such a manner as to reduce lateral displacement, therebyquickly obtaining a proper elastic image.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto stably form a high-quality elastic image even in an arbitrary timephase during an elastic image diagnosis. Further, according to thepresent invention, it is possible to stably perform high-qualityelasticity imaging with high reliability without being mislead byinformation on an insignificant elastic image frame having not beenremoved, and simultaneously it is possible to feed back causes includingan improper operating method (pressing method, etc.) to the operatorthrough an elastic image, thereby instantly making search for a pressingmethod or the like enabling a higher quality image at the site ofimaging, and providing a clinically useful ultrasound apparatus keepingits real-time property and simplicity of ultrasound imaging. Moreover,according to the present invention, it is possible to provide theoperator pressing operation information for obtaining a proper elasticimage, thereby efficiently obtaining an elastic image.

1. An ultrasound diagnostic apparatus comprising: an ultrasound probewhich transmits/receives an ultrasound wave with respect to a subject tobe diagnosed; an ultrasound wave transmit section which transmits anultrasound wave for driving the ultrasound probe; a pressing sectionwhich applies an external pressure to the subject; a displacementmeasuring section which obtains two tomographic image data different intime series from a reflected echo signal received from the ultrasoundprobe and measures a displacement of each part in the subject based onthe two tomographic image data; an image generating section whichgenerates an elastic image from elasticity information based on thedisplacement of each part measured by the displacement measuringsection; a display section which displays the generated elastic image; apressing decision section which decides whether or not the pressingoperation by the pressing section is proper based on a distribution ofthe elasticity information obtained by analyzing the displacement; and adecision output section which outputs a decision result by the pressingdecision section to the display section.
 2. The ultrasound diagnosticapparatus according to claim 1, wherein the decision output sectionoutputs through display and/or audio sound, a guidance for correctingthe pressing operation based on the decision result.
 3. The ultrasounddiagnostic apparatus according to claim 1, wherein the pressing decisionsection obtains an elastic modulus distribution in the tomographic imagedata as a distribution of the elasticity information obtained byanalyzing the displacement, and decides whether or not the pressingoperation by the pressing section is proper on the basis whether or notthe elastic modulus distribution is within a predetermined range.
 4. Theultrasound diagnostic apparatus according to claim 1, further comprisesa pressing state storing section which stores the decision result by thepressing decision section while making the decision result correspond toeach elastic image.
 5. The ultrasound diagnostic apparatus according toclaim 4, further comprises a reproduction section which make the displaysection display the elastic image stored in the pressing state storingsection, only when the pressing operation is proper.
 6. The ultrasounddiagnostic apparatus according to claim 3, wherein the pressing decisionsection obtains the elastic modulus distribution with a horizontalrepresenting the elastic modulus of each pixel and a vertical axisrepresenting the number of pixels having a uniform elastic modulus. 7.An ultrasound diagnostic apparatus comprising: an ultrasound probe whichtransmits/receives an ultrasound wave with respect to a subject to bediagnosed; an ultrasound wave transmit section which transmits anultrasound wave for driving the ultrasound probe; a pressing sectionwhich applies an external pressure to the subject; a displacementmeasuring section which obtains two tomographic image data different intime series from a reflected echo signal received from the ultrasoundprobe and measures a displacement of each part in the subject based onthe two tomographic image data; an image generating section whichgenerates an elastic image from elasticity information based on thedisplacement of each part measured by the displacement measuringsection; a display section which displays the generated elastic image; apressing decision section which obtains a degree of lateral displacementin the tomographic image data based on the displacement, and decideswhether or not the pressing operation by the pressing section is properon the basis whether or not the degree of lateral displacement is withina predetermined range; and a decision output device which outputs adecision result by the pressing decision section to the display section.8. The ultrasound diagnostic apparatus according to claim 7, wherein thedecision output section outputs through display and/or audio sound, aguidance for correcting the pressing operation based on the decisionresult.
 9. An ultrasound diagnostic apparatus comprising: an ultrasoundprobe which transmits/receives an ultrasound wave with respect to asubject to be diagnosed; an ultrasound wave transmit section whichtransmits an ultrasound wave for driving the ultrasound probe; adisplacement measuring section which obtains two tomographic image datadifferent in time series from a reflected echo signal received from theultrasound probe and measures a displacement of at least one part in thesubject caused by application of an external pressure based on the twotomographic image data; an image generating section which generates anelastic image from elasticity information based on the displacement; adisplay section which displays the generated elastic image; a pressingdecision section which decides whether or not application of theexternal pressure is proper based on a distribution of the elasticityinformation obtained by analyzing the displacement; and a decisionoutput section which outputs a decision result by the pressing decisionsection to the display section.
 10. An ultrasound diagnostic apparatuscomprising: an ultrasound probe which transmits/receives an ultrasoundwave with respect to a subject to be diagnosed; an ultrasound wavetransmit section which transmits and ultrasound wave for driving theultrasound probe; a displacement measuring section which obtains twotomographic image data different in time series from a reflected echosignal received from the ultrasound probe and measures a displacement ofat least one part in the subject caused by application of an externalpressure based on the two tomographic image data; an image generatingsection which generates an elastic image from elasticity informationbased on the displacement; a display section which displays thegenerated elastic image; a pressing decision section which obtains adegree of lateral displacement in the tomographic image data based onthe displacement, and decides whether or not the applicationdisplacement is within a proper range; and a decision output devicewhich outputs a decision result by the pressing decision section to thedisplay section.